diff --git a/internal/ceres/array_selector_test.cc b/internal/ceres/array_selector_test.cc
index f7fef3c..563fe63 100644
--- a/internal/ceres/array_selector_test.cc
+++ b/internal/ceres/array_selector_test.cc
@@ -33,8 +33,7 @@
 
 #include "gtest/gtest.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 // This test only checks, if the correct array implementations are selected. The
 // test for FixedArray is in fixed_array_test.cc. Tests for std::array and
@@ -42,38 +41,33 @@
 TEST(ArraySelector, FixedArray) {
   ArraySelector<int, DYNAMIC, 20> array1(10);
   static_assert(
-      std::is_base_of<internal::FixedArray<int, 20>, decltype(array1)>::value,
-      "");
+      std::is_base_of<internal::FixedArray<int, 20>, decltype(array1)>::value);
   EXPECT_EQ(array1.size(), 10);
 
   ArraySelector<int, DYNAMIC, 10> array2(20);
   static_assert(
-      std::is_base_of<internal::FixedArray<int, 10>, decltype(array2)>::value,
-      "");
+      std::is_base_of<internal::FixedArray<int, 10>, decltype(array2)>::value);
   EXPECT_EQ(array2.size(), 20);
 }
 
 TEST(ArraySelector, Array) {
   ArraySelector<int, 10, 20> array1(10);
-  static_assert(std::is_base_of<std::array<int, 10>, decltype(array1)>::value,
-                "");
+  static_assert(std::is_base_of<std::array<int, 10>, decltype(array1)>::value);
   EXPECT_EQ(array1.size(), 10);
 
   ArraySelector<int, 20, 20> array2(20);
-  static_assert(std::is_base_of<std::array<int, 20>, decltype(array2)>::value,
-                "");
+  static_assert(std::is_base_of<std::array<int, 20>, decltype(array2)>::value);
   EXPECT_EQ(array2.size(), 20);
 }
 
 TEST(ArraySelector, Vector) {
   ArraySelector<int, 20, 10> array1(20);
-  static_assert(std::is_base_of<std::vector<int>, decltype(array1)>::value, "");
+  static_assert(std::is_base_of<std::vector<int>, decltype(array1)>::value);
   EXPECT_EQ(array1.size(), 20);
 
   ArraySelector<int, 1, 0> array2(1);
-  static_assert(std::is_base_of<std::vector<int>, decltype(array2)>::value, "");
+  static_assert(std::is_base_of<std::vector<int>, decltype(array2)>::value);
   EXPECT_EQ(array2.size(), 1);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/array_utils.cc b/internal/ceres/array_utils.cc
index 113d41c..1501866 100644
--- a/internal/ceres/array_utils.cc
+++ b/internal/ceres/array_utils.cc
@@ -38,8 +38,7 @@
 
 #include "ceres/stringprintf.h"
 #include "ceres/types.h"
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 using std::string;
 
@@ -103,5 +102,4 @@
   }
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/array_utils.h b/internal/ceres/array_utils.h
index d2fc791..059e2d5 100644
--- a/internal/ceres/array_utils.h
+++ b/internal/ceres/array_utils.h
@@ -48,8 +48,7 @@
 #include "ceres/internal/disable_warnings.h"
 #include "ceres/internal/export.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 // Fill the array x with an impossible value that the user code is
 // never expected to compute.
@@ -85,8 +84,7 @@
 // [1 0 2 3 0 1 3]
 CERES_NO_EXPORT void MapValuesToContiguousRange(int size, int* array);
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #include "ceres/internal/reenable_warnings.h"
 
diff --git a/internal/ceres/array_utils_test.cc b/internal/ceres/array_utils_test.cc
index b011520..8a94ec1 100644
--- a/internal/ceres/array_utils_test.cc
+++ b/internal/ceres/array_utils_test.cc
@@ -36,8 +36,7 @@
 
 #include "gtest/gtest.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 using std::vector;
 
@@ -121,5 +120,4 @@
   EXPECT_EQ(array, expected);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/autodiff_cost_function_test.cc b/internal/ceres/autodiff_cost_function_test.cc
index a59d524..f4f08e6 100644
--- a/internal/ceres/autodiff_cost_function_test.cc
+++ b/internal/ceres/autodiff_cost_function_test.cc
@@ -36,8 +36,7 @@
 #include "ceres/cost_function.h"
 #include "gtest/gtest.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 class BinaryScalarCost {
  public:
@@ -179,5 +178,4 @@
   EXPECT_FALSE(IsArrayValid(2, residuals));
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/autodiff_local_parameterization_test.cc b/internal/ceres/autodiff_local_parameterization_test.cc
index 9dc2551..fc49351 100644
--- a/internal/ceres/autodiff_local_parameterization_test.cc
+++ b/internal/ceres/autodiff_local_parameterization_test.cc
@@ -36,8 +36,7 @@
 #include "ceres/rotation.h"
 #include "gtest/gtest.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 struct IdentityPlus {
   template <typename T>
@@ -223,5 +222,4 @@
   QuaternionParameterizationTestHelper(x, delta);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/autodiff_manifold_test.cc b/internal/ceres/autodiff_manifold_test.cc
index 01820c8..e8cd047 100644
--- a/internal/ceres/autodiff_manifold_test.cc
+++ b/internal/ceres/autodiff_manifold_test.cc
@@ -37,8 +37,7 @@
 #include "ceres/rotation.h"
 #include "gtest/gtest.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 namespace {
 
@@ -292,5 +291,4 @@
   }
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/autodiff_test.cc b/internal/ceres/autodiff_test.cc
index 69ce584..5f769a0 100644
--- a/internal/ceres/autodiff_test.cc
+++ b/internal/ceres/autodiff_test.cc
@@ -33,8 +33,7 @@
 #include "ceres/random.h"
 #include "gtest/gtest.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 template <typename T>
 inline T& RowMajorAccess(T* base, int rows, int cols, int i, int j) {
@@ -665,5 +664,4 @@
   x[0] = x[0] + JetT(1.0);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/block_evaluate_preparer.cc b/internal/ceres/block_evaluate_preparer.cc
index 56c97b6..ee13539 100644
--- a/internal/ceres/block_evaluate_preparer.cc
+++ b/internal/ceres/block_evaluate_preparer.cc
@@ -38,8 +38,7 @@
 #include "ceres/residual_block.h"
 #include "ceres/sparse_matrix.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 void BlockEvaluatePreparer::Init(int const* const* jacobian_layout,
                                  int max_derivatives_per_residual_block) {
@@ -78,5 +77,4 @@
   }
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/block_evaluate_preparer.h b/internal/ceres/block_evaluate_preparer.h
index d72e41b..7f3869a 100644
--- a/internal/ceres/block_evaluate_preparer.h
+++ b/internal/ceres/block_evaluate_preparer.h
@@ -39,8 +39,7 @@
 #include "ceres/internal/export.h"
 #include "ceres/scratch_evaluate_preparer.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 class ResidualBlock;
 class SparseMatrix;
@@ -72,7 +71,6 @@
   ScratchEvaluatePreparer scratch_evaluate_preparer_;
 };
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_INTERNAL_BLOCK_EVALUATE_PREPARER_H_
diff --git a/internal/ceres/block_jacobi_preconditioner.cc b/internal/ceres/block_jacobi_preconditioner.cc
index 6e979de..07d6cd3 100644
--- a/internal/ceres/block_jacobi_preconditioner.cc
+++ b/internal/ceres/block_jacobi_preconditioner.cc
@@ -36,8 +36,7 @@
 #include "ceres/casts.h"
 #include "ceres/internal/eigen.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 BlockJacobiPreconditioner::BlockJacobiPreconditioner(
     const BlockSparseMatrix& A) {
@@ -96,5 +95,4 @@
   m_->RightMultiply(x, y);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/block_jacobi_preconditioner.h b/internal/ceres/block_jacobi_preconditioner.h
index e0a512a..0928919 100644
--- a/internal/ceres/block_jacobi_preconditioner.h
+++ b/internal/ceres/block_jacobi_preconditioner.h
@@ -38,8 +38,7 @@
 #include "ceres/internal/export.h"
 #include "ceres/preconditioner.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 class BlockSparseMatrix;
 struct CompressedRowBlockStructure;
@@ -76,8 +75,7 @@
   std::unique_ptr<BlockRandomAccessDiagonalMatrix> m_;
 };
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #include "ceres/internal/reenable_warnings.h"
 
diff --git a/internal/ceres/block_jacobi_preconditioner_test.cc b/internal/ceres/block_jacobi_preconditioner_test.cc
index 06b69a2..ab69148 100644
--- a/internal/ceres/block_jacobi_preconditioner_test.cc
+++ b/internal/ceres/block_jacobi_preconditioner_test.cc
@@ -39,8 +39,7 @@
 #include "ceres/linear_least_squares_problems.h"
 #include "gtest/gtest.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 class BlockJacobiPreconditionerTest : public ::testing::Test {
  protected:
@@ -96,5 +95,4 @@
 
 TEST_F(BlockJacobiPreconditionerTest, LargeProblem) { VerifyDiagonalBlocks(3); }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/block_jacobian_writer.cc b/internal/ceres/block_jacobian_writer.cc
index a70660f..2b1742a 100644
--- a/internal/ceres/block_jacobian_writer.cc
+++ b/internal/ceres/block_jacobian_writer.cc
@@ -41,8 +41,7 @@
 #include "ceres/program.h"
 #include "ceres/residual_block.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 using std::vector;
 
@@ -209,5 +208,4 @@
   return std::make_unique<BlockSparseMatrix>(bs);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/block_jacobian_writer.h b/internal/ceres/block_jacobian_writer.h
index b2d0aaa..52fa3c4 100644
--- a/internal/ceres/block_jacobian_writer.h
+++ b/internal/ceres/block_jacobian_writer.h
@@ -44,8 +44,7 @@
 #include "ceres/evaluator.h"
 #include "ceres/internal/export.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 class BlockEvaluatePreparer;
 class Program;
@@ -124,7 +123,6 @@
   std::vector<int> jacobian_layout_storage_;
 };
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_INTERNAL_BLOCK_JACOBIAN_WRITER_H_
diff --git a/internal/ceres/block_random_access_dense_matrix.cc b/internal/ceres/block_random_access_dense_matrix.cc
index ed172de..341d7fe 100644
--- a/internal/ceres/block_random_access_dense_matrix.cc
+++ b/internal/ceres/block_random_access_dense_matrix.cc
@@ -35,8 +35,7 @@
 #include "ceres/internal/eigen.h"
 #include "glog/logging.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 BlockRandomAccessDenseMatrix::BlockRandomAccessDenseMatrix(
     const std::vector<int>& blocks) {
@@ -83,5 +82,4 @@
   }
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/block_random_access_dense_matrix.h b/internal/ceres/block_random_access_dense_matrix.h
index 171a6d6..c8c066a 100644
--- a/internal/ceres/block_random_access_dense_matrix.h
+++ b/internal/ceres/block_random_access_dense_matrix.h
@@ -38,8 +38,7 @@
 #include "ceres/internal/disable_warnings.h"
 #include "ceres/internal/export.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 // A square block random accessible matrix with the same row and
 // column block structure. All cells are stored in the same single
@@ -92,8 +91,7 @@
   std::unique_ptr<CellInfo[]> cell_infos_;
 };
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #include "ceres/internal/reenable_warnings.h"
 
diff --git a/internal/ceres/block_random_access_diagonal_matrix.cc b/internal/ceres/block_random_access_diagonal_matrix.cc
index f55f3b3..5a9f772 100644
--- a/internal/ceres/block_random_access_diagonal_matrix.cc
+++ b/internal/ceres/block_random_access_diagonal_matrix.cc
@@ -43,8 +43,7 @@
 #include "ceres/types.h"
 #include "glog/logging.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 using std::vector;
 
@@ -145,5 +144,4 @@
   }
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/block_random_access_diagonal_matrix.h b/internal/ceres/block_random_access_diagonal_matrix.h
index 3d36c37..45e3d02 100644
--- a/internal/ceres/block_random_access_diagonal_matrix.h
+++ b/internal/ceres/block_random_access_diagonal_matrix.h
@@ -42,8 +42,7 @@
 #include "ceres/triplet_sparse_matrix.h"
 #include "ceres/types.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 // A thread safe block diagonal matrix implementation of
 // BlockRandomAccessMatrix.
@@ -96,8 +95,7 @@
   friend class BlockRandomAccessDiagonalMatrixTest;
 };
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #include "ceres/internal/reenable_warnings.h"
 
diff --git a/internal/ceres/block_random_access_matrix.cc b/internal/ceres/block_random_access_matrix.cc
index 8e70c04..eeaef79 100644
--- a/internal/ceres/block_random_access_matrix.cc
+++ b/internal/ceres/block_random_access_matrix.cc
@@ -30,10 +30,8 @@
 
 #include "ceres/block_random_access_matrix.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 BlockRandomAccessMatrix::~BlockRandomAccessMatrix() = default;
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/block_random_access_matrix.h b/internal/ceres/block_random_access_matrix.h
index 48759b7..600f59d 100644
--- a/internal/ceres/block_random_access_matrix.h
+++ b/internal/ceres/block_random_access_matrix.h
@@ -37,8 +37,7 @@
 
 #include "ceres/internal/export.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 // A matrix implementing the BlockRandomAccessMatrix interface is a
 // matrix whose rows and columns are divided into blocks. For example
@@ -123,7 +122,6 @@
   virtual int num_cols() const = 0;
 };
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_INTERNAL_BLOCK_RANDOM_ACCESS_MATRIX_H_
diff --git a/internal/ceres/block_random_access_sparse_matrix.cc b/internal/ceres/block_random_access_sparse_matrix.cc
index a026daa..3ae0cba 100644
--- a/internal/ceres/block_random_access_sparse_matrix.cc
+++ b/internal/ceres/block_random_access_sparse_matrix.cc
@@ -41,8 +41,7 @@
 #include "ceres/types.h"
 #include "glog/logging.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 using std::make_pair;
 using std::pair;
@@ -127,8 +126,7 @@
                                                  int* col,
                                                  int* row_stride,
                                                  int* col_stride) {
-  const LayoutType::iterator it =
-      layout_.find(IntPairToLong(row_block_id, col_block_id));
+  const auto it = layout_.find(IntPairToLong(row_block_id, col_block_id));
   if (it == layout_.end()) {
     return nullptr;
   }
@@ -182,5 +180,4 @@
   }
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/block_random_access_sparse_matrix.h b/internal/ceres/block_random_access_sparse_matrix.h
index b31a2ad..882292c 100644
--- a/internal/ceres/block_random_access_sparse_matrix.h
+++ b/internal/ceres/block_random_access_sparse_matrix.h
@@ -45,8 +45,7 @@
 #include "ceres/triplet_sparse_matrix.h"
 #include "ceres/types.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 // A thread safe square block sparse implementation of
 // BlockRandomAccessMatrix. Internally a TripletSparseMatrix is used
@@ -125,8 +124,7 @@
   friend class BlockRandomAccessSparseMatrixTest;
 };
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #include "ceres/internal/reenable_warnings.h"
 
diff --git a/internal/ceres/block_sparse_matrix.cc b/internal/ceres/block_sparse_matrix.cc
index 31ea39d..9ba054f 100644
--- a/internal/ceres/block_sparse_matrix.cc
+++ b/internal/ceres/block_sparse_matrix.cc
@@ -42,8 +42,7 @@
 #include "ceres/triplet_sparse_matrix.h"
 #include "glog/logging.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 using std::vector;
 
@@ -404,5 +403,4 @@
   return matrix;
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/block_sparse_matrix.h b/internal/ceres/block_sparse_matrix.h
index 75b0deb..987a435 100644
--- a/internal/ceres/block_sparse_matrix.h
+++ b/internal/ceres/block_sparse_matrix.h
@@ -42,8 +42,7 @@
 #include "ceres/internal/export.h"
 #include "ceres/sparse_matrix.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 class TripletSparseMatrix;
 
@@ -158,8 +157,7 @@
   const double* values_;
 };
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #include "ceres/internal/reenable_warnings.h"
 
diff --git a/internal/ceres/block_structure.cc b/internal/ceres/block_structure.cc
index 39ba082..f6767b4 100644
--- a/internal/ceres/block_structure.cc
+++ b/internal/ceres/block_structure.cc
@@ -30,8 +30,7 @@
 
 #include "ceres/block_structure.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 bool CellLessThan(const Cell& lhs, const Cell& rhs) {
   if (lhs.block_id == rhs.block_id) {
@@ -40,5 +39,4 @@
   return (lhs.block_id < rhs.block_id);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/block_structure.h b/internal/ceres/block_structure.h
index fe7574c..52b7b2f 100644
--- a/internal/ceres/block_structure.h
+++ b/internal/ceres/block_structure.h
@@ -43,8 +43,7 @@
 
 #include "ceres/internal/export.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 using BlockSize = int32_t;
 
@@ -93,7 +92,6 @@
   std::vector<CompressedColumn> cols;
 };
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_INTERNAL_BLOCK_STRUCTURE_H_
diff --git a/internal/ceres/callbacks.cc b/internal/ceres/callbacks.cc
index 7a4381c..fcdcb2a 100644
--- a/internal/ceres/callbacks.cc
+++ b/internal/ceres/callbacks.cc
@@ -37,8 +37,7 @@
 #include "ceres/stringprintf.h"
 #include "glog/logging.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 using std::string;
 
@@ -127,5 +126,4 @@
   return SOLVER_CONTINUE;
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/callbacks.h b/internal/ceres/callbacks.h
index 3b1d10c..b22f5ff 100644
--- a/internal/ceres/callbacks.h
+++ b/internal/ceres/callbacks.h
@@ -36,8 +36,7 @@
 #include "ceres/internal/export.h"
 #include "ceres/iteration_callback.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 class Program;
 
@@ -84,7 +83,6 @@
   const bool log_to_stdout_;
 };
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_INTERNAL_CALLBACKS_H_
diff --git a/internal/ceres/canonical_views_clustering.cc b/internal/ceres/canonical_views_clustering.cc
index 01b8ad3..7c385fc 100644
--- a/internal/ceres/canonical_views_clustering.cc
+++ b/internal/ceres/canonical_views_clustering.cc
@@ -39,8 +39,7 @@
 #include "ceres/map_util.h"
 #include "glog/logging.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 using std::vector;
 
@@ -222,5 +221,4 @@
   }
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/canonical_views_clustering.h b/internal/ceres/canonical_views_clustering.h
index 00a6a73..6325f2e 100644
--- a/internal/ceres/canonical_views_clustering.h
+++ b/internal/ceres/canonical_views_clustering.h
@@ -48,8 +48,7 @@
 #include "ceres/internal/disable_warnings.h"
 #include "ceres/internal/export.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 struct CanonicalViewsClusteringOptions;
 
@@ -120,8 +119,7 @@
   double view_score_weight = 0.0;
 };
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #include "ceres/internal/reenable_warnings.h"
 
diff --git a/internal/ceres/canonical_views_clustering_test.cc b/internal/ceres/canonical_views_clustering_test.cc
index 0593d65..31ba6e0 100644
--- a/internal/ceres/canonical_views_clustering_test.cc
+++ b/internal/ceres/canonical_views_clustering_test.cc
@@ -36,8 +36,7 @@
 #include "ceres/graph.h"
 #include "gtest/gtest.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 const int kVertexIds[] = {0, 1, 2, 3};
 class CanonicalViewsTest : public ::testing::Test {
@@ -139,5 +138,4 @@
   EXPECT_EQ(centers_[0], kVertexIds[1]);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/cgnr_linear_operator.h b/internal/ceres/cgnr_linear_operator.h
index d708efc..4e47aff 100644
--- a/internal/ceres/cgnr_linear_operator.h
+++ b/internal/ceres/cgnr_linear_operator.h
@@ -39,8 +39,7 @@
 #include "ceres/internal/export.h"
 #include "ceres/linear_operator.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 class SparseMatrix;
 
@@ -115,8 +114,7 @@
   std::unique_ptr<double[]> z_;
 };
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #include "ceres/internal/reenable_warnings.h"
 
diff --git a/internal/ceres/cgnr_solver.cc b/internal/ceres/cgnr_solver.cc
index cca72bc..c7cf4f8 100644
--- a/internal/ceres/cgnr_solver.cc
+++ b/internal/ceres/cgnr_solver.cc
@@ -42,8 +42,7 @@
 #include "ceres/wall_time.h"
 #include "glog/logging.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 CgnrSolver::CgnrSolver(LinearSolver::Options options)
     : options_(std::move(options)) {
@@ -108,5 +107,4 @@
   return summary;
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/cgnr_solver.h b/internal/ceres/cgnr_solver.h
index 25e62e9..119f838 100644
--- a/internal/ceres/cgnr_solver.h
+++ b/internal/ceres/cgnr_solver.h
@@ -36,8 +36,7 @@
 #include "ceres/internal/export.h"
 #include "ceres/linear_solver.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 class Preconditioner;
 
@@ -67,7 +66,6 @@
   std::unique_ptr<Preconditioner> preconditioner_;
 };
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_INTERNAL_CGNR_SOLVER_H_
diff --git a/internal/ceres/compressed_col_sparse_matrix_utils.cc b/internal/ceres/compressed_col_sparse_matrix_utils.cc
index 94e7e9a..cb6be55 100644
--- a/internal/ceres/compressed_col_sparse_matrix_utils.cc
+++ b/internal/ceres/compressed_col_sparse_matrix_utils.cc
@@ -36,8 +36,7 @@
 #include "ceres/internal/export.h"
 #include "glog/logging.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 using std::vector;
 
@@ -71,7 +70,7 @@
   for (int col_block = 0; col_block < num_col_blocks; ++col_block) {
     int column_size = 0;
     for (int idx = scalar_cols[c]; idx < scalar_cols[c + 1]; ++idx) {
-      vector<int>::const_iterator it = std::lower_bound(
+      auto it = std::lower_bound(
           row_block_starts.begin(), row_block_starts.end(), scalar_rows[idx]);
       // Since we are using lower_bound, it will return the row id
       // where the row block starts. For everything but the first row
@@ -118,5 +117,4 @@
     }
   }
 }
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/compressed_col_sparse_matrix_utils.h b/internal/ceres/compressed_col_sparse_matrix_utils.h
index f88a5bd..608150e 100644
--- a/internal/ceres/compressed_col_sparse_matrix_utils.h
+++ b/internal/ceres/compressed_col_sparse_matrix_utils.h
@@ -37,8 +37,7 @@
 #include "ceres/internal/disable_warnings.h"
 #include "ceres/internal/export.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 // Extract the block sparsity pattern of the scalar compressed columns
 // matrix and return it in compressed column form. The compressed
@@ -141,8 +140,7 @@
   SolveUpperTriangularInPlace(num_cols, rows, cols, values, solution);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #include "ceres/internal/reenable_warnings.h"
 
diff --git a/internal/ceres/compressed_row_jacobian_writer.cc b/internal/ceres/compressed_row_jacobian_writer.cc
index 55b30a2..c409872 100644
--- a/internal/ceres/compressed_row_jacobian_writer.cc
+++ b/internal/ceres/compressed_row_jacobian_writer.cc
@@ -44,8 +44,7 @@
 #include "ceres/residual_block.h"
 #include "ceres/scratch_evaluate_preparer.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 using std::adjacent_find;
 using std::make_pair;
@@ -238,5 +237,4 @@
   }
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/compressed_row_jacobian_writer.h b/internal/ceres/compressed_row_jacobian_writer.h
index 7badab7..d8cf795 100644
--- a/internal/ceres/compressed_row_jacobian_writer.h
+++ b/internal/ceres/compressed_row_jacobian_writer.h
@@ -41,8 +41,7 @@
 #include "ceres/internal/export.h"
 #include "ceres/scratch_evaluate_preparer.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 class CompressedRowSparseMatrix;
 class Program;
@@ -107,7 +106,6 @@
   Program* program_;
 };
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_INTERNAL_COMPRESSED_ROW_JACOBIAN_WRITER_H_
diff --git a/internal/ceres/compressed_row_sparse_matrix.cc b/internal/ceres/compressed_row_sparse_matrix.cc
index db103d9..7a08c6f 100644
--- a/internal/ceres/compressed_row_sparse_matrix.cc
+++ b/internal/ceres/compressed_row_sparse_matrix.cc
@@ -41,8 +41,7 @@
 #include "ceres/triplet_sparse_matrix.h"
 #include "glog/logging.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 using std::vector;
 
@@ -733,5 +732,4 @@
   return matrix;
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/concurrent_queue.h b/internal/ceres/concurrent_queue.h
index 1e74153..207bc8e 100644
--- a/internal/ceres/concurrent_queue.h
+++ b/internal/ceres/concurrent_queue.h
@@ -38,8 +38,7 @@
 
 #include "glog/logging.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 // A thread-safe multi-producer, multi-consumer queue for queueing items that
 // are typically handled asynchronously by multiple threads. The ConcurrentQueue
@@ -152,7 +151,6 @@
   bool wait_{true};
 };
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_INTERNAL_CONCURRENT_QUEUE_H_
diff --git a/internal/ceres/concurrent_queue_test.cc b/internal/ceres/concurrent_queue_test.cc
index 99be5f2..b0930fe 100644
--- a/internal/ceres/concurrent_queue_test.cc
+++ b/internal/ceres/concurrent_queue_test.cc
@@ -40,8 +40,7 @@
 #include "gmock/gmock.h"
 #include "gtest/gtest.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 // A basic test of push and pop.
 TEST(ConcurrentQueue, PushPop) {
@@ -300,7 +299,6 @@
   EXPECT_EQ(13456, value);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_USE_CXX_THREADS
diff --git a/internal/ceres/conjugate_gradients_solver.cc b/internal/ceres/conjugate_gradients_solver.cc
index 62ae920..2888173 100644
--- a/internal/ceres/conjugate_gradients_solver.cc
+++ b/internal/ceres/conjugate_gradients_solver.cc
@@ -49,8 +49,7 @@
 #include "ceres/types.h"
 #include "glog/logging.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 namespace {
 
 bool IsZeroOrInfinity(double x) { return ((x == 0.0) || std::isinf(x)); }
@@ -249,5 +248,4 @@
   return summary;
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/conjugate_gradients_solver.h b/internal/ceres/conjugate_gradients_solver.h
index 99ddb5d..1ea9646 100644
--- a/internal/ceres/conjugate_gradients_solver.h
+++ b/internal/ceres/conjugate_gradients_solver.h
@@ -38,8 +38,7 @@
 #include "ceres/internal/export.h"
 #include "ceres/linear_solver.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 class LinearOperator;
 
@@ -68,8 +67,7 @@
   const LinearSolver::Options options_;
 };
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #include "ceres/internal/reenable_warnings.h"
 
diff --git a/internal/ceres/conjugate_gradients_solver_test.cc b/internal/ceres/conjugate_gradients_solver_test.cc
index b11e522..badad04 100644
--- a/internal/ceres/conjugate_gradients_solver_test.cc
+++ b/internal/ceres/conjugate_gradients_solver_test.cc
@@ -41,8 +41,7 @@
 #include "ceres/types.h"
 #include "gtest/gtest.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST(ConjugateGradientTest, Solves3x3IdentitySystem) {
   double diagonal[] = {1.0, 1.0, 1.0};
@@ -132,5 +131,4 @@
   ASSERT_DOUBLE_EQ(2, x(2));
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/context_impl.cc b/internal/ceres/context_impl.cc
index a4b3c84..decee3b 100644
--- a/internal/ceres/context_impl.cc
+++ b/internal/ceres/context_impl.cc
@@ -40,8 +40,7 @@
 #include "cusolverDn.h"
 #endif  // CERES_NO_CUDA
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 ContextImpl::ContextImpl() = default;
 
@@ -104,5 +103,4 @@
   thread_pool.Resize(num_threads);
 #endif  // CERES_USE_CXX_THREADS
 }
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/context_impl.h b/internal/ceres/context_impl.h
index 8e9a03f..3bcb2b5 100644
--- a/internal/ceres/context_impl.h
+++ b/internal/ceres/context_impl.h
@@ -52,8 +52,7 @@
 #include "ceres/thread_pool.h"
 #endif  // CERES_USE_CXX_THREADS
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 class CERES_NO_EXPORT ContextImpl final : public Context {
  public:
@@ -89,8 +88,7 @@
 #endif  // CERES_NO_CUDA
 };
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #include "ceres/internal/reenable_warnings.h"
 
diff --git a/internal/ceres/coordinate_descent_minimizer.cc b/internal/ceres/coordinate_descent_minimizer.cc
index a6e149d..298b604 100644
--- a/internal/ceres/coordinate_descent_minimizer.cc
+++ b/internal/ceres/coordinate_descent_minimizer.cc
@@ -49,8 +49,7 @@
 #include "ceres/trust_region_minimizer.h"
 #include "ceres/trust_region_strategy.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 using std::map;
 using std::max;
@@ -270,5 +269,4 @@
   return ordering;
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/coordinate_descent_minimizer.h b/internal/ceres/coordinate_descent_minimizer.h
index 75f2648..7c27f8c 100644
--- a/internal/ceres/coordinate_descent_minimizer.h
+++ b/internal/ceres/coordinate_descent_minimizer.h
@@ -40,8 +40,7 @@
 #include "ceres/problem_impl.h"
 #include "ceres/solver.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 class Program;
 class LinearSolver;
@@ -103,7 +102,6 @@
   ContextImpl* context_;
 };
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_INTERNAL_COORDINATE_DESCENT_MINIMIZER_H_
diff --git a/internal/ceres/corrector.cc b/internal/ceres/corrector.cc
index bf3ba9c..a84c442 100644
--- a/internal/ceres/corrector.cc
+++ b/internal/ceres/corrector.cc
@@ -36,8 +36,7 @@
 #include "ceres/internal/eigen.h"
 #include "glog/logging.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 Corrector::Corrector(const double sq_norm, const double rho[3]) {
   CHECK_GE(sq_norm, 0.0);
@@ -155,5 +154,4 @@
   }
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/corrector.h b/internal/ceres/corrector.h
index 44379a3..b6997b1 100644
--- a/internal/ceres/corrector.h
+++ b/internal/ceres/corrector.h
@@ -38,8 +38,7 @@
 #include "ceres/internal/disable_warnings.h"
 #include "ceres/internal/export.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 // Corrector is responsible for applying the second order correction
 // to the residual and jacobian of a least squares problem based on a
@@ -87,8 +86,7 @@
   double residual_scaling_;
   double alpha_sq_norm_;
 };
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #include "ceres/internal/reenable_warnings.h"
 
diff --git a/internal/ceres/cost_function_to_functor_test.cc b/internal/ceres/cost_function_to_functor_test.cc
index dfa1a92..f26fc1d 100644
--- a/internal/ceres/cost_function_to_functor_test.cc
+++ b/internal/ceres/cost_function_to_functor_test.cc
@@ -38,8 +38,7 @@
 #include "ceres/dynamic_cost_function_to_functor.h"
 #include "gtest/gtest.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 using std::vector;
 const double kTolerance = 1e-18;
@@ -392,5 +391,4 @@
   ExpectCostFunctionsAreEqual(cost_function, *actual_cost_function);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/covariance_impl.cc b/internal/ceres/covariance_impl.cc
index ef0aac0..9e1bfaa 100644
--- a/internal/ceres/covariance_impl.cc
+++ b/internal/ceres/covariance_impl.cc
@@ -57,8 +57,7 @@
 #include "ceres/wall_time.h"
 #include "glog/logging.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 using std::swap;
 
@@ -901,5 +900,4 @@
   return true;
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/covariance_impl.h b/internal/ceres/covariance_impl.h
index fc029ce..a32bd4f 100644
--- a/internal/ceres/covariance_impl.h
+++ b/internal/ceres/covariance_impl.h
@@ -43,8 +43,7 @@
 #include "ceres/problem_impl.h"
 #include "ceres/suitesparse.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 class CompressedRowSparseMatrix;
 
@@ -96,8 +95,7 @@
   std::unique_ptr<CompressedRowSparseMatrix> covariance_matrix_;
 };
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #include "ceres/internal/reenable_warnings.h"
 
diff --git a/internal/ceres/cubic_interpolation_test.cc b/internal/ceres/cubic_interpolation_test.cc
index 03b1aae..0200568 100644
--- a/internal/ceres/cubic_interpolation_test.cc
+++ b/internal/ceres/cubic_interpolation_test.cc
@@ -36,8 +36,7 @@
 #include "glog/logging.h"
 #include "gtest/gtest.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 static constexpr double kTolerance = 1e-12;
 
@@ -530,5 +529,4 @@
               kTolerance);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/cuda_dense_qr_test.cc b/internal/ceres/cuda_dense_qr_test.cc
index 9b4d375..4df79bd 100644
--- a/internal/ceres/cuda_dense_qr_test.cc
+++ b/internal/ceres/cuda_dense_qr_test.cc
@@ -35,8 +35,7 @@
 #include "glog/logging.h"
 #include "gtest/gtest.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 #ifndef CERES_NO_CUDA
 
@@ -164,5 +163,4 @@
 }
 #endif  // CERES_NO_CUDA
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/cxsparse.cc b/internal/ceres/cxsparse.cc
index b1eb205..9dd797f 100644
--- a/internal/ceres/cxsparse.cc
+++ b/internal/ceres/cxsparse.cc
@@ -43,8 +43,7 @@
 #include "ceres/triplet_sparse_matrix.h"
 #include "glog/logging.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 using std::vector;
 
@@ -278,7 +277,6 @@
   }
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_NO_CXSPARSE
diff --git a/internal/ceres/cxsparse.h b/internal/ceres/cxsparse.h
index 97fc045..f4f1e4e 100644
--- a/internal/ceres/cxsparse.h
+++ b/internal/ceres/cxsparse.h
@@ -45,8 +45,7 @@
 #include "ceres/sparse_cholesky.h"
 #include "cs.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 class CompressedRowSparseMatrix;
 class TripletSparseMatrix;
@@ -164,8 +163,7 @@
   csn* numeric_factor_;
 };
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #include "ceres/internal/reenable_warnings.h"
 
diff --git a/internal/ceres/dense_cholesky.cc b/internal/ceres/dense_cholesky.cc
index 0e0bba7..dec0de1 100644
--- a/internal/ceres/dense_cholesky.cc
+++ b/internal/ceres/dense_cholesky.cc
@@ -59,8 +59,7 @@
                         int* info);
 #endif
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 DenseCholesky::~DenseCholesky() = default;
 
@@ -323,5 +322,4 @@
 
 #endif  // CERES_NO_CUDA
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/dense_cholesky.h b/internal/ceres/dense_cholesky.h
index 655a2f8..5866d38 100644
--- a/internal/ceres/dense_cholesky.h
+++ b/internal/ceres/dense_cholesky.h
@@ -49,8 +49,7 @@
 #include "cusolverDn.h"
 #endif  // CERES_NO_CUDA
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 // An interface that abstracts away the internal details of various dense linear
 // algebra libraries and offers a simple API for solving dense symmetric
@@ -177,7 +176,6 @@
 
 #endif  // CERES_NO_CUDA
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_INTERNAL_DENSE_CHOLESKY_H_
diff --git a/internal/ceres/dense_cholesky_test.cc b/internal/ceres/dense_cholesky_test.cc
index 42b746e..59ee9f7 100644
--- a/internal/ceres/dense_cholesky_test.cc
+++ b/internal/ceres/dense_cholesky_test.cc
@@ -43,8 +43,7 @@
 #include "gmock/gmock.h"
 #include "gtest/gtest.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 using Param = DenseLinearAlgebraLibraryType;
 
@@ -118,5 +117,4 @@
 
 INSTANTIATE_TEST_SUITE_P(_, DenseCholeskyTest, MakeValues(), ParamInfoToString);
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/dense_linear_solver_benchmark.cc b/internal/ceres/dense_linear_solver_benchmark.cc
index 665200a..53628ad 100644
--- a/internal/ceres/dense_linear_solver_benchmark.cc
+++ b/internal/ceres/dense_linear_solver_benchmark.cc
@@ -36,8 +36,7 @@
 #include "ceres/linear_solver.h"
 #include "ceres/random.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 template <ceres::DenseLinearAlgebraLibraryType kLibraryType,
           ceres::LinearSolverType kSolverType>
@@ -105,7 +104,6 @@
     ->Apply(MatrixSizes);
 #endif  // CERES_NO_CUDA
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 BENCHMARK_MAIN();
diff --git a/internal/ceres/dense_linear_solver_test.cc b/internal/ceres/dense_linear_solver_test.cc
index aa2afc8..8c662cd 100644
--- a/internal/ceres/dense_linear_solver_test.cc
+++ b/internal/ceres/dense_linear_solver_test.cc
@@ -40,8 +40,7 @@
 #include "glog/logging.h"
 #include "gtest/gtest.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 using Param = ::testing::
     tuple<LinearSolverType, DenseLinearAlgebraLibraryType, bool, int>;
@@ -136,5 +135,4 @@
 
 #endif
 }  // namespace
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/dense_normal_cholesky_solver.cc b/internal/ceres/dense_normal_cholesky_solver.cc
index 30a0c02..2865dd8 100644
--- a/internal/ceres/dense_normal_cholesky_solver.cc
+++ b/internal/ceres/dense_normal_cholesky_solver.cc
@@ -39,8 +39,7 @@
 #include "ceres/types.h"
 #include "ceres/wall_time.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 DenseNormalCholeskySolver::DenseNormalCholeskySolver(
     LinearSolver::Options options)
@@ -87,5 +86,4 @@
   return summary;
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/dense_normal_cholesky_solver.h b/internal/ceres/dense_normal_cholesky_solver.h
index 5b3c740..f27fea0 100644
--- a/internal/ceres/dense_normal_cholesky_solver.h
+++ b/internal/ceres/dense_normal_cholesky_solver.h
@@ -41,8 +41,7 @@
 #include "ceres/internal/export.h"
 #include "ceres/linear_solver.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 class DenseSparseMatrix;
 
@@ -94,8 +93,7 @@
   std::unique_ptr<DenseCholesky> cholesky_;
 };
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #include "ceres/internal/reenable_warnings.h"
 
diff --git a/internal/ceres/dense_qr.cc b/internal/ceres/dense_qr.cc
index 4b9c8a4..8d02368 100644
--- a/internal/ceres/dense_qr.cc
+++ b/internal/ceres/dense_qr.cc
@@ -108,8 +108,7 @@
 
 #endif
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 DenseQR::~DenseQR() = default;
 
@@ -477,5 +476,4 @@
 
 #endif  // CERES_NO_CUDA
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/dense_qr.h b/internal/ceres/dense_qr.h
index 7a2ffb5..6992563 100644
--- a/internal/ceres/dense_qr.h
+++ b/internal/ceres/dense_qr.h
@@ -54,8 +54,7 @@
 #include "cusolverDn.h"
 #endif  // CERES_NO_CUDA
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 // An interface that abstracts away the internal details of various dense linear
 // algebra libraries and offers a simple API for solving dense linear systems
@@ -199,8 +198,7 @@
 
 #endif  // CERES_NO_CUDA
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #include "ceres/internal/reenable_warnings.h"
 
diff --git a/internal/ceres/dense_qr_solver.cc b/internal/ceres/dense_qr_solver.cc
index 24cb25a..abce57c 100644
--- a/internal/ceres/dense_qr_solver.cc
+++ b/internal/ceres/dense_qr_solver.cc
@@ -40,8 +40,7 @@
 #include "ceres/types.h"
 #include "ceres/wall_time.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 DenseQRSolver::DenseQRSolver(const LinearSolver::Options& options)
     : options_(options), dense_qr_(DenseQR::Create(options)) {}
@@ -81,5 +80,4 @@
   return summary;
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/dense_qr_solver.h b/internal/ceres/dense_qr_solver.h
index 39922a2..e95d59d 100644
--- a/internal/ceres/dense_qr_solver.h
+++ b/internal/ceres/dense_qr_solver.h
@@ -40,8 +40,7 @@
 #include "ceres/internal/export.h"
 #include "ceres/linear_solver.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 class DenseSparseMatrix;
 
@@ -112,8 +111,7 @@
   std::unique_ptr<DenseQR> dense_qr_;
 };
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #include "ceres/internal/reenable_warnings.h"
 
diff --git a/internal/ceres/dense_qr_test.cc b/internal/ceres/dense_qr_test.cc
index 199e033..6c0ad31 100644
--- a/internal/ceres/dense_qr_test.cc
+++ b/internal/ceres/dense_qr_test.cc
@@ -43,8 +43,7 @@
 #include "gmock/gmock.h"
 #include "gtest/gtest.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 using Param = DenseLinearAlgebraLibraryType;
 
@@ -123,5 +122,4 @@
 
 INSTANTIATE_TEST_SUITE_P(_, DenseQRTest, MakeValues(), ParamInfoToString);
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/dense_sparse_matrix.cc b/internal/ceres/dense_sparse_matrix.cc
index 8b967f2..cef219f 100644
--- a/internal/ceres/dense_sparse_matrix.cc
+++ b/internal/ceres/dense_sparse_matrix.cc
@@ -38,8 +38,7 @@
 #include "ceres/triplet_sparse_matrix.h"
 #include "glog/logging.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 DenseSparseMatrix::DenseSparseMatrix(int num_rows, int num_cols)
     : m_(Matrix(num_rows, num_cols)) {}
@@ -100,5 +99,4 @@
   }
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/dense_sparse_matrix.h b/internal/ceres/dense_sparse_matrix.h
index 655cbb8..160a591 100644
--- a/internal/ceres/dense_sparse_matrix.h
+++ b/internal/ceres/dense_sparse_matrix.h
@@ -39,8 +39,7 @@
 #include "ceres/sparse_matrix.h"
 #include "ceres/types.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 class TripletSparseMatrix;
 
@@ -73,8 +72,7 @@
   Matrix m_;
 };
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #include "ceres/internal/reenable_warnings.h"
 
diff --git a/internal/ceres/dense_sparse_matrix_test.cc b/internal/ceres/dense_sparse_matrix_test.cc
index 1bfd6c6..6bce0b4 100644
--- a/internal/ceres/dense_sparse_matrix_test.cc
+++ b/internal/ceres/dense_sparse_matrix_test.cc
@@ -43,8 +43,7 @@
 #include "glog/logging.h"
 #include "gtest/gtest.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 static void CompareMatrices(const SparseMatrix* a, const SparseMatrix* b) {
   EXPECT_EQ(a->num_rows(), b->num_rows());
@@ -166,5 +165,4 @@
   EXPECT_EQ((tsm_dense - dsm_dense).norm(), 0.0);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/detect_structure.cc b/internal/ceres/detect_structure.cc
index 4aac445..ebf6aee 100644
--- a/internal/ceres/detect_structure.cc
+++ b/internal/ceres/detect_structure.cc
@@ -33,8 +33,7 @@
 #include "ceres/internal/eigen.h"
 #include "glog/logging.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 void DetectStructure(const CompressedRowBlockStructure& bs,
                      const int num_eliminate_blocks,
@@ -119,5 +118,4 @@
   // clang-format on
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/detect_structure.h b/internal/ceres/detect_structure.h
index 6151c04..78b6c50 100644
--- a/internal/ceres/detect_structure.h
+++ b/internal/ceres/detect_structure.h
@@ -35,8 +35,7 @@
 #include "ceres/internal/disable_warnings.h"
 #include "ceres/internal/export.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 // Detect static blocks in the problem sparsity. For rows containing
 // e_blocks, we are interested in detecting if the size of the row
@@ -63,8 +62,7 @@
                                      int* e_block_size,
                                      int* f_block_size);
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #include "ceres/internal/reenable_warnings.h"
 
diff --git a/internal/ceres/dogleg_strategy.cc b/internal/ceres/dogleg_strategy.cc
index 65f7ccd..c9369c2 100644
--- a/internal/ceres/dogleg_strategy.cc
+++ b/internal/ceres/dogleg_strategy.cc
@@ -44,8 +44,7 @@
 #include "ceres/types.h"
 #include "glog/logging.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 namespace {
 const double kMaxMu = 1.0;
 const double kMinMu = 1e-8;
@@ -710,5 +709,4 @@
   return true;
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/dogleg_strategy.h b/internal/ceres/dogleg_strategy.h
index 1d219af..d2f6b01 100644
--- a/internal/ceres/dogleg_strategy.h
+++ b/internal/ceres/dogleg_strategy.h
@@ -36,8 +36,7 @@
 #include "ceres/linear_solver.h"
 #include "ceres/trust_region_strategy.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 // Dogleg step computation and trust region sizing strategy based on
 // on "Methods for Nonlinear Least Squares" by K. Madsen, H.B. Nielsen
@@ -159,8 +158,7 @@
   Matrix2d subspace_B_;
 };
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #include "ceres/internal/reenable_warnings.h"
 
diff --git a/internal/ceres/dogleg_strategy_test.cc b/internal/ceres/dogleg_strategy_test.cc
index cd5fe02..d1ef611 100644
--- a/internal/ceres/dogleg_strategy_test.cc
+++ b/internal/ceres/dogleg_strategy_test.cc
@@ -40,8 +40,7 @@
 #include "glog/logging.h"
 #include "gtest/gtest.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 namespace {
 
 class Fixture : public testing::Test {
@@ -275,5 +274,4 @@
   EXPECT_NEAR(x_(5), 0.0, kToleranceLoose);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/dynamic_autodiff_cost_function_test.cc b/internal/ceres/dynamic_autodiff_cost_function_test.cc
index 7ee820a..6777d0c 100644
--- a/internal/ceres/dynamic_autodiff_cost_function_test.cc
+++ b/internal/ceres/dynamic_autodiff_cost_function_test.cc
@@ -37,8 +37,7 @@
 
 #include "gtest/gtest.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 using std::vector;
 
@@ -805,5 +804,4 @@
   EXPECT_EQ(residual, target_value);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/dynamic_compressed_row_finalizer.h b/internal/ceres/dynamic_compressed_row_finalizer.h
index fedee3b..ebb3839 100644
--- a/internal/ceres/dynamic_compressed_row_finalizer.h
+++ b/internal/ceres/dynamic_compressed_row_finalizer.h
@@ -35,8 +35,7 @@
 #include "ceres/dynamic_compressed_row_sparse_matrix.h"
 #include "ceres/internal/export.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 struct CERES_NO_EXPORT DynamicCompressedRowJacobianFinalizer {
   void operator()(SparseMatrix* base_jacobian, int num_parameters) {
@@ -46,7 +45,6 @@
   }
 };
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_INTERNAL_DYNAMIC_COMPRESED_ROW_FINALISER_H_
diff --git a/internal/ceres/dynamic_compressed_row_jacobian_writer.cc b/internal/ceres/dynamic_compressed_row_jacobian_writer.cc
index 8c254e9..a97c333 100644
--- a/internal/ceres/dynamic_compressed_row_jacobian_writer.cc
+++ b/internal/ceres/dynamic_compressed_row_jacobian_writer.cc
@@ -39,8 +39,7 @@
 #include "ceres/program.h"
 #include "ceres/residual_block.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 using std::pair;
 using std::vector;
@@ -100,5 +99,4 @@
   }
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/dynamic_compressed_row_jacobian_writer.h b/internal/ceres/dynamic_compressed_row_jacobian_writer.h
index 794a9b4..42ac05b 100644
--- a/internal/ceres/dynamic_compressed_row_jacobian_writer.h
+++ b/internal/ceres/dynamic_compressed_row_jacobian_writer.h
@@ -40,8 +40,7 @@
 #include "ceres/internal/export.h"
 #include "ceres/scratch_evaluate_preparer.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 class Program;
 class SparseMatrix;
@@ -80,7 +79,6 @@
   Program* program_;
 };
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_INTERNAL_DYNAMIC_COMPRESSED_ROW_JACOBIAN_WRITER_H_
diff --git a/internal/ceres/dynamic_compressed_row_sparse_matrix.cc b/internal/ceres/dynamic_compressed_row_sparse_matrix.cc
index 7185e14..6fcf9e4 100644
--- a/internal/ceres/dynamic_compressed_row_sparse_matrix.cc
+++ b/internal/ceres/dynamic_compressed_row_sparse_matrix.cc
@@ -32,8 +32,7 @@
 
 #include <cstring>
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 DynamicCompressedRowSparseMatrix::DynamicCompressedRowSparseMatrix(
     int num_rows, int num_cols, int initial_max_num_nonzeros)
@@ -99,5 +98,4 @@
       << "the number of jacobian nonzeros. Please contact the developers!";
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/dynamic_compressed_row_sparse_matrix.h b/internal/ceres/dynamic_compressed_row_sparse_matrix.h
index 5b4c402..0094f7e 100644
--- a/internal/ceres/dynamic_compressed_row_sparse_matrix.h
+++ b/internal/ceres/dynamic_compressed_row_sparse_matrix.h
@@ -47,8 +47,7 @@
 #include "ceres/internal/disable_warnings.h"
 #include "ceres/internal/export.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 class CERES_NO_EXPORT DynamicCompressedRowSparseMatrix final
     : public CompressedRowSparseMatrix {
@@ -98,8 +97,7 @@
   std::vector<std::vector<double>> dynamic_values_;
 };
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #include "ceres/internal/reenable_warnings.h"
 
diff --git a/internal/ceres/dynamic_numeric_diff_cost_function_test.cc b/internal/ceres/dynamic_numeric_diff_cost_function_test.cc
index e35e1bc..f2a37e3 100644
--- a/internal/ceres/dynamic_numeric_diff_cost_function_test.cc
+++ b/internal/ceres/dynamic_numeric_diff_cost_function_test.cc
@@ -36,8 +36,7 @@
 
 #include "gtest/gtest.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 using std::vector;
 
@@ -510,5 +509,4 @@
   }
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/dynamic_sparse_normal_cholesky_solver.cc b/internal/ceres/dynamic_sparse_normal_cholesky_solver.cc
index 5e907e1..61c402b 100644
--- a/internal/ceres/dynamic_sparse_normal_cholesky_solver.cc
+++ b/internal/ceres/dynamic_sparse_normal_cholesky_solver.cc
@@ -52,8 +52,7 @@
 #include "Eigen/SparseCholesky"
 #endif
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 DynamicSparseNormalCholeskySolver::DynamicSparseNormalCholeskySolver(
     LinearSolver::Options options)
@@ -285,5 +284,4 @@
 #endif
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/dynamic_sparse_normal_cholesky_solver.h b/internal/ceres/dynamic_sparse_normal_cholesky_solver.h
index 6f73c96..d3591a2 100644
--- a/internal/ceres/dynamic_sparse_normal_cholesky_solver.h
+++ b/internal/ceres/dynamic_sparse_normal_cholesky_solver.h
@@ -42,8 +42,7 @@
 #include "ceres/internal/export.h"
 #include "ceres/linear_solver.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 class CompressedRowSparseMatrix;
 
@@ -77,7 +76,6 @@
   const LinearSolver::Options options_;
 };
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_INTERNAL_DYNAMIC_SPARSE_NORMAL_CHOLESKY_SOLVER_H_
diff --git a/internal/ceres/dynamic_sparsity_test.cc b/internal/ceres/dynamic_sparsity_test.cc
index 8c98528..29cfb15 100644
--- a/internal/ceres/dynamic_sparsity_test.cc
+++ b/internal/ceres/dynamic_sparsity_test.cc
@@ -39,8 +39,7 @@
 #include "glog/logging.h"
 #include "gtest/gtest.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 // Data generated with the following Python code.
 //   import numpy as np
@@ -454,5 +453,4 @@
       << dynamic_summary.FullReport();
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/eigensparse.cc b/internal/ceres/eigensparse.cc
index 81668c8..c1b7cc6 100644
--- a/internal/ceres/eigensparse.cc
+++ b/internal/ceres/eigensparse.cc
@@ -41,8 +41,7 @@
 #include "ceres/compressed_row_sparse_matrix.h"
 #include "ceres/linear_solver.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 // TODO(sameeragarwal): Use enable_if to clean up the implementations
 // for when Scalar == double.
@@ -177,7 +176,6 @@
 
 FloatEigenSparseCholesky::~FloatEigenSparseCholesky() = default;
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_USE_EIGEN_SPARSE
diff --git a/internal/ceres/eigensparse.h b/internal/ceres/eigensparse.h
index c4a4142..e1a6b96 100644
--- a/internal/ceres/eigensparse.h
+++ b/internal/ceres/eigensparse.h
@@ -46,8 +46,7 @@
 #include "ceres/linear_solver.h"
 #include "ceres/sparse_cholesky.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 class CERES_NO_EXPORT EigenSparseCholesky : public SparseCholesky {
  public:
@@ -83,8 +82,7 @@
                                     std::string* message) override = 0;
 };
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_USE_EIGEN_SPARSE
 
diff --git a/internal/ceres/evaluation_callback_test.cc b/internal/ceres/evaluation_callback_test.cc
index 179c106..59b03d4 100644
--- a/internal/ceres/evaluation_callback_test.cc
+++ b/internal/ceres/evaluation_callback_test.cc
@@ -42,8 +42,7 @@
 #include "ceres/solver.h"
 #include "gtest/gtest.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 // Use an inline hash function to avoid portability wrangling. Algorithm from
 // Daniel Bernstein, known as the "djb2" hash.
@@ -386,5 +385,4 @@
   WithLineSearchMinimizerImpl(ARMIJO, NONLINEAR_CONJUGATE_GRADIENT, QUADRATIC);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/evaluator.cc b/internal/ceres/evaluator.cc
index 52d0f09..f44796a 100644
--- a/internal/ceres/evaluator.cc
+++ b/internal/ceres/evaluator.cc
@@ -46,8 +46,7 @@
 #include "ceres/scratch_evaluate_preparer.h"
 #include "glog/logging.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 Evaluator::~Evaluator() = default;
 
@@ -88,5 +87,4 @@
   }
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/evaluator_test_utils.cc b/internal/ceres/evaluator_test_utils.cc
index f3384bc..a0ef84a 100644
--- a/internal/ceres/evaluator_test_utils.cc
+++ b/internal/ceres/evaluator_test_utils.cc
@@ -34,8 +34,7 @@
 #include "ceres/internal/eigen.h"
 #include "gtest/gtest.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 void CompareEvaluations(int expected_num_rows,
                         int expected_num_cols,
@@ -88,5 +87,4 @@
   }
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/evaluator_test_utils.h b/internal/ceres/evaluator_test_utils.h
index c9661f1..799588c 100644
--- a/internal/ceres/evaluator_test_utils.h
+++ b/internal/ceres/evaluator_test_utils.h
@@ -33,8 +33,7 @@
 
 #include "ceres/internal/export.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 // Fixed sized struct for storing an evaluation.
 struct CERES_NO_EXPORT ExpectedEvaluation {
@@ -58,5 +57,4 @@
                                         const double* actual_gradient,
                                         const double* actual_jacobian);
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/execution_summary.h b/internal/ceres/execution_summary.h
index fbee75f..b71418c 100644
--- a/internal/ceres/execution_summary.h
+++ b/internal/ceres/execution_summary.h
@@ -39,8 +39,7 @@
 #include "ceres/internal/export.h"
 #include "ceres/wall_time.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 struct CallStatistics {
   CallStatistics() = default;
@@ -85,7 +84,6 @@
   ExecutionSummary* summary_;
 };
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_INTERNAL_EXECUTION_SUMMARY_H_
diff --git a/internal/ceres/file.cc b/internal/ceres/file.cc
index 94f2135..cd91843 100644
--- a/internal/ceres/file.cc
+++ b/internal/ceres/file.cc
@@ -36,8 +36,7 @@
 
 #include "glog/logging.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 using std::string;
 
@@ -90,5 +89,4 @@
   }
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/file.h b/internal/ceres/file.h
index bd13128..d88dd2a 100644
--- a/internal/ceres/file.h
+++ b/internal/ceres/file.h
@@ -38,8 +38,7 @@
 #include "ceres/internal/disable_warnings.h"
 #include "ceres/internal/export.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 CERES_NO_EXPORT
 void WriteStringToFileOrDie(const std::string& data,
@@ -52,8 +51,7 @@
 CERES_NO_EXPORT
 std::string JoinPath(const std::string& dirname, const std::string& basename);
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #include "ceres/internal/reenable_warnings.h"
 
diff --git a/internal/ceres/float_cxsparse.cc b/internal/ceres/float_cxsparse.cc
index a6d5e81..f675307 100644
--- a/internal/ceres/float_cxsparse.cc
+++ b/internal/ceres/float_cxsparse.cc
@@ -34,8 +34,7 @@
 
 #if !defined(CERES_NO_CXSPARSE)
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 std::unique_ptr<SparseCholesky> FloatCXSparseCholesky::Create(
     OrderingType ordering_type) {
@@ -43,7 +42,6 @@
   return {};
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // !defined(CERES_NO_CXSPARSE)
diff --git a/internal/ceres/float_cxsparse.h b/internal/ceres/float_cxsparse.h
index 8b4514a..9c559d2 100644
--- a/internal/ceres/float_cxsparse.h
+++ b/internal/ceres/float_cxsparse.h
@@ -41,8 +41,7 @@
 #include "ceres/internal/export.h"
 #include "ceres/sparse_cholesky.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 // Fake implementation of a single precision Sparse Cholesky using
 // CXSparse.
@@ -51,8 +50,7 @@
   static std::unique_ptr<SparseCholesky> Create(OrderingType ordering_type);
 };
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // !defined(CERES_NO_CXSPARSE)
 
diff --git a/internal/ceres/float_suitesparse.cc b/internal/ceres/float_suitesparse.cc
index dc1d0e4..e08639b 100644
--- a/internal/ceres/float_suitesparse.cc
+++ b/internal/ceres/float_suitesparse.cc
@@ -34,8 +34,7 @@
 
 #if !defined(CERES_NO_SUITESPARSE)
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 std::unique_ptr<SparseCholesky> FloatSuiteSparseCholesky::Create(
     OrderingType ordering_type) {
@@ -43,7 +42,6 @@
   return {};
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // !defined(CERES_NO_SUITESPARSE)
diff --git a/internal/ceres/float_suitesparse.h b/internal/ceres/float_suitesparse.h
index 7e76799..3b18a42 100644
--- a/internal/ceres/float_suitesparse.h
+++ b/internal/ceres/float_suitesparse.h
@@ -43,8 +43,7 @@
 
 #if !defined(CERES_NO_SUITESPARSE)
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 // Fake implementation of a single precision Sparse Cholesky using
 // SuiteSparse.
@@ -53,8 +52,7 @@
   static std::unique_ptr<SparseCholesky> Create(OrderingType ordering_type);
 };
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // !defined(CERES_NO_SUITESPARSE)
 
diff --git a/internal/ceres/function_sample.cc b/internal/ceres/function_sample.cc
index 3e0ae60..d80ab34 100644
--- a/internal/ceres/function_sample.cc
+++ b/internal/ceres/function_sample.cc
@@ -32,8 +32,7 @@
 
 #include "ceres/stringprintf.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 FunctionSample::FunctionSample()
     : x(0.0),
@@ -75,5 +74,4 @@
       gradient_is_valid);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/function_sample.h b/internal/ceres/function_sample.h
index 63ffc8f..85074c2 100644
--- a/internal/ceres/function_sample.h
+++ b/internal/ceres/function_sample.h
@@ -37,8 +37,7 @@
 #include "ceres/internal/eigen.h"
 #include "ceres/internal/export.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 // FunctionSample is used by the line search routines to store and
 // communicate the value and (optionally) the gradient of the function
@@ -88,8 +87,7 @@
   bool gradient_is_valid;
 };
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #include "ceres/internal/reenable_warnings.h"
 
diff --git a/internal/ceres/generate_bundle_adjustment_tests.py b/internal/ceres/generate_bundle_adjustment_tests.py
index 2c93e37..566258b 100644
--- a/internal/ceres/generate_bundle_adjustment_tests.py
+++ b/internal/ceres/generate_bundle_adjustment_tests.py
@@ -139,8 +139,7 @@
 #include "ceres/internal/config.h"
 #include "bundle_adjustment_test_util.h"
 %(preprocessor_conditions_begin)s
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
        %(test_class_name)s) {  // NOLINT
@@ -158,8 +157,7 @@
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 %(preprocessor_conditions_end)s""")
 
 def camelcasify(token):
@@ -267,7 +265,7 @@
     fd.write(BUNDLE_ADJUSTMENT_TEST_TEMPLATE % template_parameters)
 
   # All done.
-  print 'Generated', filename
+  print('Generated', filename)
 
   return filename
 
diff --git a/internal/ceres/generated/partitioned_matrix_view_2_2_2.cc b/internal/ceres/generated/partitioned_matrix_view_2_2_2.cc
index 7b4ed16..c950f17 100644
--- a/internal/ceres/generated/partitioned_matrix_view_2_2_2.cc
+++ b/internal/ceres/generated/partitioned_matrix_view_2_2_2.cc
@@ -46,12 +46,10 @@
 
 #include "ceres/partitioned_matrix_view_impl.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 template class PartitionedMatrixView<2, 2, 2>;
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_RESTRICT_SCHUR_SPECIALIZATION
diff --git a/internal/ceres/generated/partitioned_matrix_view_2_2_3.cc b/internal/ceres/generated/partitioned_matrix_view_2_2_3.cc
index 0f01251..7092852 100644
--- a/internal/ceres/generated/partitioned_matrix_view_2_2_3.cc
+++ b/internal/ceres/generated/partitioned_matrix_view_2_2_3.cc
@@ -46,12 +46,10 @@
 
 #include "ceres/partitioned_matrix_view_impl.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 template class PartitionedMatrixView<2, 2, 3>;
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_RESTRICT_SCHUR_SPECIALIZATION
diff --git a/internal/ceres/generated/partitioned_matrix_view_2_2_4.cc b/internal/ceres/generated/partitioned_matrix_view_2_2_4.cc
index bdbe91c..89c7067 100644
--- a/internal/ceres/generated/partitioned_matrix_view_2_2_4.cc
+++ b/internal/ceres/generated/partitioned_matrix_view_2_2_4.cc
@@ -46,12 +46,10 @@
 
 #include "ceres/partitioned_matrix_view_impl.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 template class PartitionedMatrixView<2, 2, 4>;
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_RESTRICT_SCHUR_SPECIALIZATION
diff --git a/internal/ceres/generated/partitioned_matrix_view_2_2_d.cc b/internal/ceres/generated/partitioned_matrix_view_2_2_d.cc
index 71f293b..94d5499 100644
--- a/internal/ceres/generated/partitioned_matrix_view_2_2_d.cc
+++ b/internal/ceres/generated/partitioned_matrix_view_2_2_d.cc
@@ -46,12 +46,10 @@
 
 #include "ceres/partitioned_matrix_view_impl.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 template class PartitionedMatrixView<2, 2, Eigen::Dynamic>;
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_RESTRICT_SCHUR_SPECIALIZATION
diff --git a/internal/ceres/generated/partitioned_matrix_view_2_3_3.cc b/internal/ceres/generated/partitioned_matrix_view_2_3_3.cc
index a6ea776..be07d9e 100644
--- a/internal/ceres/generated/partitioned_matrix_view_2_3_3.cc
+++ b/internal/ceres/generated/partitioned_matrix_view_2_3_3.cc
@@ -46,12 +46,10 @@
 
 #include "ceres/partitioned_matrix_view_impl.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 template class PartitionedMatrixView<2, 3, 3>;
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_RESTRICT_SCHUR_SPECIALIZATION
diff --git a/internal/ceres/generated/partitioned_matrix_view_2_3_4.cc b/internal/ceres/generated/partitioned_matrix_view_2_3_4.cc
index e712678..a065392 100644
--- a/internal/ceres/generated/partitioned_matrix_view_2_3_4.cc
+++ b/internal/ceres/generated/partitioned_matrix_view_2_3_4.cc
@@ -46,12 +46,10 @@
 
 #include "ceres/partitioned_matrix_view_impl.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 template class PartitionedMatrixView<2, 3, 4>;
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_RESTRICT_SCHUR_SPECIALIZATION
diff --git a/internal/ceres/generated/partitioned_matrix_view_2_3_6.cc b/internal/ceres/generated/partitioned_matrix_view_2_3_6.cc
index 3aff26e..9e69b3e 100644
--- a/internal/ceres/generated/partitioned_matrix_view_2_3_6.cc
+++ b/internal/ceres/generated/partitioned_matrix_view_2_3_6.cc
@@ -46,12 +46,10 @@
 
 #include "ceres/partitioned_matrix_view_impl.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 template class PartitionedMatrixView<2, 3, 6>;
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_RESTRICT_SCHUR_SPECIALIZATION
diff --git a/internal/ceres/generated/partitioned_matrix_view_2_3_9.cc b/internal/ceres/generated/partitioned_matrix_view_2_3_9.cc
index 6cd239b..3af3194 100644
--- a/internal/ceres/generated/partitioned_matrix_view_2_3_9.cc
+++ b/internal/ceres/generated/partitioned_matrix_view_2_3_9.cc
@@ -46,12 +46,10 @@
 
 #include "ceres/partitioned_matrix_view_impl.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 template class PartitionedMatrixView<2, 3, 9>;
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_RESTRICT_SCHUR_SPECIALIZATION
diff --git a/internal/ceres/generated/partitioned_matrix_view_2_3_d.cc b/internal/ceres/generated/partitioned_matrix_view_2_3_d.cc
index 68c5055..52aeb47 100644
--- a/internal/ceres/generated/partitioned_matrix_view_2_3_d.cc
+++ b/internal/ceres/generated/partitioned_matrix_view_2_3_d.cc
@@ -46,12 +46,10 @@
 
 #include "ceres/partitioned_matrix_view_impl.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 template class PartitionedMatrixView<2, 3, Eigen::Dynamic>;
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_RESTRICT_SCHUR_SPECIALIZATION
diff --git a/internal/ceres/generated/partitioned_matrix_view_2_4_3.cc b/internal/ceres/generated/partitioned_matrix_view_2_4_3.cc
index 88c5e29..beded65 100644
--- a/internal/ceres/generated/partitioned_matrix_view_2_4_3.cc
+++ b/internal/ceres/generated/partitioned_matrix_view_2_4_3.cc
@@ -46,12 +46,10 @@
 
 #include "ceres/partitioned_matrix_view_impl.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 template class PartitionedMatrixView<2, 4, 3>;
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_RESTRICT_SCHUR_SPECIALIZATION
diff --git a/internal/ceres/generated/partitioned_matrix_view_2_4_4.cc b/internal/ceres/generated/partitioned_matrix_view_2_4_4.cc
index b948783..74ee39e 100644
--- a/internal/ceres/generated/partitioned_matrix_view_2_4_4.cc
+++ b/internal/ceres/generated/partitioned_matrix_view_2_4_4.cc
@@ -46,12 +46,10 @@
 
 #include "ceres/partitioned_matrix_view_impl.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 template class PartitionedMatrixView<2, 4, 4>;
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_RESTRICT_SCHUR_SPECIALIZATION
diff --git a/internal/ceres/generated/partitioned_matrix_view_2_4_6.cc b/internal/ceres/generated/partitioned_matrix_view_2_4_6.cc
index 7f044ef..1b71f50 100644
--- a/internal/ceres/generated/partitioned_matrix_view_2_4_6.cc
+++ b/internal/ceres/generated/partitioned_matrix_view_2_4_6.cc
@@ -46,12 +46,10 @@
 
 #include "ceres/partitioned_matrix_view_impl.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 template class PartitionedMatrixView<2, 4, 6>;
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_RESTRICT_SCHUR_SPECIALIZATION
diff --git a/internal/ceres/generated/partitioned_matrix_view_2_4_8.cc b/internal/ceres/generated/partitioned_matrix_view_2_4_8.cc
index 7394e79..e6fdbb3 100644
--- a/internal/ceres/generated/partitioned_matrix_view_2_4_8.cc
+++ b/internal/ceres/generated/partitioned_matrix_view_2_4_8.cc
@@ -46,12 +46,10 @@
 
 #include "ceres/partitioned_matrix_view_impl.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 template class PartitionedMatrixView<2, 4, 8>;
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_RESTRICT_SCHUR_SPECIALIZATION
diff --git a/internal/ceres/generated/partitioned_matrix_view_2_4_9.cc b/internal/ceres/generated/partitioned_matrix_view_2_4_9.cc
index 263f1fb..4452286 100644
--- a/internal/ceres/generated/partitioned_matrix_view_2_4_9.cc
+++ b/internal/ceres/generated/partitioned_matrix_view_2_4_9.cc
@@ -46,12 +46,10 @@
 
 #include "ceres/partitioned_matrix_view_impl.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 template class PartitionedMatrixView<2, 4, 9>;
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_RESTRICT_SCHUR_SPECIALIZATION
diff --git a/internal/ceres/generated/partitioned_matrix_view_2_4_d.cc b/internal/ceres/generated/partitioned_matrix_view_2_4_d.cc
index d47634e..9ab4e22 100644
--- a/internal/ceres/generated/partitioned_matrix_view_2_4_d.cc
+++ b/internal/ceres/generated/partitioned_matrix_view_2_4_d.cc
@@ -46,12 +46,10 @@
 
 #include "ceres/partitioned_matrix_view_impl.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 template class PartitionedMatrixView<2, 4, Eigen::Dynamic>;
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_RESTRICT_SCHUR_SPECIALIZATION
diff --git a/internal/ceres/generated/partitioned_matrix_view_2_d_d.cc b/internal/ceres/generated/partitioned_matrix_view_2_d_d.cc
index 0944cdc..01223aa 100644
--- a/internal/ceres/generated/partitioned_matrix_view_2_d_d.cc
+++ b/internal/ceres/generated/partitioned_matrix_view_2_d_d.cc
@@ -46,12 +46,10 @@
 
 #include "ceres/partitioned_matrix_view_impl.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 template class PartitionedMatrixView<2, Eigen::Dynamic, Eigen::Dynamic>;
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_RESTRICT_SCHUR_SPECIALIZATION
diff --git a/internal/ceres/generated/partitioned_matrix_view_3_3_3.cc b/internal/ceres/generated/partitioned_matrix_view_3_3_3.cc
index 2367403..28f43bb 100644
--- a/internal/ceres/generated/partitioned_matrix_view_3_3_3.cc
+++ b/internal/ceres/generated/partitioned_matrix_view_3_3_3.cc
@@ -46,12 +46,10 @@
 
 #include "ceres/partitioned_matrix_view_impl.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 template class PartitionedMatrixView<3, 3, 3>;
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_RESTRICT_SCHUR_SPECIALIZATION
diff --git a/internal/ceres/generated/partitioned_matrix_view_4_4_2.cc b/internal/ceres/generated/partitioned_matrix_view_4_4_2.cc
index d5268ca..e8c65c2 100644
--- a/internal/ceres/generated/partitioned_matrix_view_4_4_2.cc
+++ b/internal/ceres/generated/partitioned_matrix_view_4_4_2.cc
@@ -46,12 +46,10 @@
 
 #include "ceres/partitioned_matrix_view_impl.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 template class PartitionedMatrixView<4, 4, 2>;
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_RESTRICT_SCHUR_SPECIALIZATION
diff --git a/internal/ceres/generated/partitioned_matrix_view_4_4_3.cc b/internal/ceres/generated/partitioned_matrix_view_4_4_3.cc
index 67e098f..a56d8af 100644
--- a/internal/ceres/generated/partitioned_matrix_view_4_4_3.cc
+++ b/internal/ceres/generated/partitioned_matrix_view_4_4_3.cc
@@ -46,12 +46,10 @@
 
 #include "ceres/partitioned_matrix_view_impl.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 template class PartitionedMatrixView<4, 4, 3>;
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_RESTRICT_SCHUR_SPECIALIZATION
diff --git a/internal/ceres/generated/partitioned_matrix_view_4_4_4.cc b/internal/ceres/generated/partitioned_matrix_view_4_4_4.cc
index 5fe28ca..fd27396 100644
--- a/internal/ceres/generated/partitioned_matrix_view_4_4_4.cc
+++ b/internal/ceres/generated/partitioned_matrix_view_4_4_4.cc
@@ -46,12 +46,10 @@
 
 #include "ceres/partitioned_matrix_view_impl.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 template class PartitionedMatrixView<4, 4, 4>;
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_RESTRICT_SCHUR_SPECIALIZATION
diff --git a/internal/ceres/generated/partitioned_matrix_view_4_4_d.cc b/internal/ceres/generated/partitioned_matrix_view_4_4_d.cc
index d87c76d..fd756c4 100644
--- a/internal/ceres/generated/partitioned_matrix_view_4_4_d.cc
+++ b/internal/ceres/generated/partitioned_matrix_view_4_4_d.cc
@@ -46,12 +46,10 @@
 
 #include "ceres/partitioned_matrix_view_impl.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 template class PartitionedMatrixView<4, 4, Eigen::Dynamic>;
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_RESTRICT_SCHUR_SPECIALIZATION
diff --git a/internal/ceres/generated/partitioned_matrix_view_d_d_d.cc b/internal/ceres/generated/partitioned_matrix_view_d_d_d.cc
index 1e12479..a7d67b5 100644
--- a/internal/ceres/generated/partitioned_matrix_view_d_d_d.cc
+++ b/internal/ceres/generated/partitioned_matrix_view_d_d_d.cc
@@ -41,12 +41,10 @@
 
 #include "ceres/partitioned_matrix_view_impl.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 template class PartitionedMatrixView<Eigen::Dynamic,
                                      Eigen::Dynamic,
                                      Eigen::Dynamic>;
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/generated/schur_eliminator_2_2_2.cc b/internal/ceres/generated/schur_eliminator_2_2_2.cc
index dc47a2e..39a4a05 100644
--- a/internal/ceres/generated/schur_eliminator_2_2_2.cc
+++ b/internal/ceres/generated/schur_eliminator_2_2_2.cc
@@ -46,12 +46,10 @@
 
 #include "ceres/schur_eliminator_impl.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 template class SchurEliminator<2, 2, 2>;
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_RESTRICT_SCHUR_SPECIALIZATION
diff --git a/internal/ceres/generated/schur_eliminator_2_2_3.cc b/internal/ceres/generated/schur_eliminator_2_2_3.cc
index e2df6f6..32c120c 100644
--- a/internal/ceres/generated/schur_eliminator_2_2_3.cc
+++ b/internal/ceres/generated/schur_eliminator_2_2_3.cc
@@ -46,12 +46,10 @@
 
 #include "ceres/schur_eliminator_impl.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 template class SchurEliminator<2, 2, 3>;
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_RESTRICT_SCHUR_SPECIALIZATION
diff --git a/internal/ceres/generated/schur_eliminator_2_2_4.cc b/internal/ceres/generated/schur_eliminator_2_2_4.cc
index 0b1ae94..afe1ff2 100644
--- a/internal/ceres/generated/schur_eliminator_2_2_4.cc
+++ b/internal/ceres/generated/schur_eliminator_2_2_4.cc
@@ -46,12 +46,10 @@
 
 #include "ceres/schur_eliminator_impl.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 template class SchurEliminator<2, 2, 4>;
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_RESTRICT_SCHUR_SPECIALIZATION
diff --git a/internal/ceres/generated/schur_eliminator_2_2_d.cc b/internal/ceres/generated/schur_eliminator_2_2_d.cc
index 0f7b6d7..ea98816 100644
--- a/internal/ceres/generated/schur_eliminator_2_2_d.cc
+++ b/internal/ceres/generated/schur_eliminator_2_2_d.cc
@@ -46,12 +46,10 @@
 
 #include "ceres/schur_eliminator_impl.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 template class SchurEliminator<2, 2, Eigen::Dynamic>;
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_RESTRICT_SCHUR_SPECIALIZATION
diff --git a/internal/ceres/generated/schur_eliminator_2_3_3.cc b/internal/ceres/generated/schur_eliminator_2_3_3.cc
index e4ab8eb..5506575 100644
--- a/internal/ceres/generated/schur_eliminator_2_3_3.cc
+++ b/internal/ceres/generated/schur_eliminator_2_3_3.cc
@@ -46,12 +46,10 @@
 
 #include "ceres/schur_eliminator_impl.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 template class SchurEliminator<2, 3, 3>;
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_RESTRICT_SCHUR_SPECIALIZATION
diff --git a/internal/ceres/generated/schur_eliminator_2_3_4.cc b/internal/ceres/generated/schur_eliminator_2_3_4.cc
index d73d466..1c4abb0 100644
--- a/internal/ceres/generated/schur_eliminator_2_3_4.cc
+++ b/internal/ceres/generated/schur_eliminator_2_3_4.cc
@@ -46,12 +46,10 @@
 
 #include "ceres/schur_eliminator_impl.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 template class SchurEliminator<2, 3, 4>;
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_RESTRICT_SCHUR_SPECIALIZATION
diff --git a/internal/ceres/generated/schur_eliminator_2_3_6.cc b/internal/ceres/generated/schur_eliminator_2_3_6.cc
index 800ee53..2dbe5f1 100644
--- a/internal/ceres/generated/schur_eliminator_2_3_6.cc
+++ b/internal/ceres/generated/schur_eliminator_2_3_6.cc
@@ -46,12 +46,10 @@
 
 #include "ceres/schur_eliminator_impl.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 template class SchurEliminator<2, 3, 6>;
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_RESTRICT_SCHUR_SPECIALIZATION
diff --git a/internal/ceres/generated/schur_eliminator_2_3_9.cc b/internal/ceres/generated/schur_eliminator_2_3_9.cc
index d38cd56..7cb73e8 100644
--- a/internal/ceres/generated/schur_eliminator_2_3_9.cc
+++ b/internal/ceres/generated/schur_eliminator_2_3_9.cc
@@ -46,12 +46,10 @@
 
 #include "ceres/schur_eliminator_impl.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 template class SchurEliminator<2, 3, 9>;
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_RESTRICT_SCHUR_SPECIALIZATION
diff --git a/internal/ceres/generated/schur_eliminator_2_3_d.cc b/internal/ceres/generated/schur_eliminator_2_3_d.cc
index 4ac4b8a..1d07e4b 100644
--- a/internal/ceres/generated/schur_eliminator_2_3_d.cc
+++ b/internal/ceres/generated/schur_eliminator_2_3_d.cc
@@ -46,12 +46,10 @@
 
 #include "ceres/schur_eliminator_impl.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 template class SchurEliminator<2, 3, Eigen::Dynamic>;
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_RESTRICT_SCHUR_SPECIALIZATION
diff --git a/internal/ceres/generated/schur_eliminator_2_4_3.cc b/internal/ceres/generated/schur_eliminator_2_4_3.cc
index d5f5dbe..35a51f9 100644
--- a/internal/ceres/generated/schur_eliminator_2_4_3.cc
+++ b/internal/ceres/generated/schur_eliminator_2_4_3.cc
@@ -46,12 +46,10 @@
 
 #include "ceres/schur_eliminator_impl.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 template class SchurEliminator<2, 4, 3>;
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_RESTRICT_SCHUR_SPECIALIZATION
diff --git a/internal/ceres/generated/schur_eliminator_2_4_4.cc b/internal/ceres/generated/schur_eliminator_2_4_4.cc
index d50a6d4..e1d8099 100644
--- a/internal/ceres/generated/schur_eliminator_2_4_4.cc
+++ b/internal/ceres/generated/schur_eliminator_2_4_4.cc
@@ -46,12 +46,10 @@
 
 #include "ceres/schur_eliminator_impl.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 template class SchurEliminator<2, 4, 4>;
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_RESTRICT_SCHUR_SPECIALIZATION
diff --git a/internal/ceres/generated/schur_eliminator_2_4_6.cc b/internal/ceres/generated/schur_eliminator_2_4_6.cc
index f79fa4d..b694e10 100644
--- a/internal/ceres/generated/schur_eliminator_2_4_6.cc
+++ b/internal/ceres/generated/schur_eliminator_2_4_6.cc
@@ -46,12 +46,10 @@
 
 #include "ceres/schur_eliminator_impl.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 template class SchurEliminator<2, 4, 6>;
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_RESTRICT_SCHUR_SPECIALIZATION
diff --git a/internal/ceres/generated/schur_eliminator_2_4_8.cc b/internal/ceres/generated/schur_eliminator_2_4_8.cc
index 972b000..251faa5 100644
--- a/internal/ceres/generated/schur_eliminator_2_4_8.cc
+++ b/internal/ceres/generated/schur_eliminator_2_4_8.cc
@@ -46,12 +46,10 @@
 
 #include "ceres/schur_eliminator_impl.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 template class SchurEliminator<2, 4, 8>;
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_RESTRICT_SCHUR_SPECIALIZATION
diff --git a/internal/ceres/generated/schur_eliminator_2_4_9.cc b/internal/ceres/generated/schur_eliminator_2_4_9.cc
index aa33e47..d935b20 100644
--- a/internal/ceres/generated/schur_eliminator_2_4_9.cc
+++ b/internal/ceres/generated/schur_eliminator_2_4_9.cc
@@ -46,12 +46,10 @@
 
 #include "ceres/schur_eliminator_impl.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 template class SchurEliminator<2, 4, 9>;
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_RESTRICT_SCHUR_SPECIALIZATION
diff --git a/internal/ceres/generated/schur_eliminator_2_4_d.cc b/internal/ceres/generated/schur_eliminator_2_4_d.cc
index a28ef15..63ee516 100644
--- a/internal/ceres/generated/schur_eliminator_2_4_d.cc
+++ b/internal/ceres/generated/schur_eliminator_2_4_d.cc
@@ -46,12 +46,10 @@
 
 #include "ceres/schur_eliminator_impl.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 template class SchurEliminator<2, 4, Eigen::Dynamic>;
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_RESTRICT_SCHUR_SPECIALIZATION
diff --git a/internal/ceres/generated/schur_eliminator_2_d_d.cc b/internal/ceres/generated/schur_eliminator_2_d_d.cc
index 4392427..25fc2c2 100644
--- a/internal/ceres/generated/schur_eliminator_2_d_d.cc
+++ b/internal/ceres/generated/schur_eliminator_2_d_d.cc
@@ -46,12 +46,10 @@
 
 #include "ceres/schur_eliminator_impl.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 template class SchurEliminator<2, Eigen::Dynamic, Eigen::Dynamic>;
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_RESTRICT_SCHUR_SPECIALIZATION
diff --git a/internal/ceres/generated/schur_eliminator_3_3_3.cc b/internal/ceres/generated/schur_eliminator_3_3_3.cc
index 7ff2a62..b4e2f98 100644
--- a/internal/ceres/generated/schur_eliminator_3_3_3.cc
+++ b/internal/ceres/generated/schur_eliminator_3_3_3.cc
@@ -46,12 +46,10 @@
 
 #include "ceres/schur_eliminator_impl.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 template class SchurEliminator<3, 3, 3>;
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_RESTRICT_SCHUR_SPECIALIZATION
diff --git a/internal/ceres/generated/schur_eliminator_4_4_2.cc b/internal/ceres/generated/schur_eliminator_4_4_2.cc
index 9008b81..c39e8aa 100644
--- a/internal/ceres/generated/schur_eliminator_4_4_2.cc
+++ b/internal/ceres/generated/schur_eliminator_4_4_2.cc
@@ -46,12 +46,10 @@
 
 #include "ceres/schur_eliminator_impl.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 template class SchurEliminator<4, 4, 2>;
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_RESTRICT_SCHUR_SPECIALIZATION
diff --git a/internal/ceres/generated/schur_eliminator_4_4_3.cc b/internal/ceres/generated/schur_eliminator_4_4_3.cc
index 8e37df5..7c360fe 100644
--- a/internal/ceres/generated/schur_eliminator_4_4_3.cc
+++ b/internal/ceres/generated/schur_eliminator_4_4_3.cc
@@ -46,12 +46,10 @@
 
 #include "ceres/schur_eliminator_impl.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 template class SchurEliminator<4, 4, 3>;
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_RESTRICT_SCHUR_SPECIALIZATION
diff --git a/internal/ceres/generated/schur_eliminator_4_4_4.cc b/internal/ceres/generated/schur_eliminator_4_4_4.cc
index 09d5081..bddd58d 100644
--- a/internal/ceres/generated/schur_eliminator_4_4_4.cc
+++ b/internal/ceres/generated/schur_eliminator_4_4_4.cc
@@ -46,12 +46,10 @@
 
 #include "ceres/schur_eliminator_impl.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 template class SchurEliminator<4, 4, 4>;
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_RESTRICT_SCHUR_SPECIALIZATION
diff --git a/internal/ceres/generated/schur_eliminator_4_4_d.cc b/internal/ceres/generated/schur_eliminator_4_4_d.cc
index 089df2d..c33f300 100644
--- a/internal/ceres/generated/schur_eliminator_4_4_d.cc
+++ b/internal/ceres/generated/schur_eliminator_4_4_d.cc
@@ -46,12 +46,10 @@
 
 #include "ceres/schur_eliminator_impl.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 template class SchurEliminator<4, 4, Eigen::Dynamic>;
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_RESTRICT_SCHUR_SPECIALIZATION
diff --git a/internal/ceres/generated/schur_eliminator_d_d_d.cc b/internal/ceres/generated/schur_eliminator_d_d_d.cc
index ca598fe..bcde11a 100644
--- a/internal/ceres/generated/schur_eliminator_d_d_d.cc
+++ b/internal/ceres/generated/schur_eliminator_d_d_d.cc
@@ -41,10 +41,8 @@
 
 #include "ceres/schur_eliminator_impl.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 template class SchurEliminator<Eigen::Dynamic, Eigen::Dynamic, Eigen::Dynamic>;
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_denseschur_cuda_auto_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_denseschur_cuda_auto_test.cc
index 3a032c5..1e3cc52 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_denseschur_cuda_auto_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_denseschur_cuda_auto_test.cc
@@ -40,8 +40,7 @@
 
 #ifndef CERES_NO_CUDA
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
        DenseSchur_Cuda_AutomaticOrdering) {  // NOLINT
@@ -59,7 +58,6 @@
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_NO_CUDA
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_denseschur_cuda_auto_threads_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_denseschur_cuda_auto_threads_test.cc
index fa0d1e7..d0181e3 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_denseschur_cuda_auto_threads_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_denseschur_cuda_auto_threads_test.cc
@@ -41,8 +41,7 @@
 #ifndef CERES_NO_CUDA
 #ifndef CERES_NO_THREADS
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
        DenseSchur_Cuda_AutomaticOrdering_Threads) {  // NOLINT
@@ -60,8 +59,7 @@
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_NO_THREADS
 #endif  // CERES_NO_CUDA
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_denseschur_cuda_user_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_denseschur_cuda_user_test.cc
index e735769..53a7aa0 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_denseschur_cuda_user_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_denseschur_cuda_user_test.cc
@@ -40,8 +40,7 @@
 
 #ifndef CERES_NO_CUDA
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
        DenseSchur_Cuda_UserOrdering) {  // NOLINT
@@ -59,7 +58,6 @@
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_NO_CUDA
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_denseschur_cuda_user_threads_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_denseschur_cuda_user_threads_test.cc
index 6473efc..ecda17c 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_denseschur_cuda_user_threads_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_denseschur_cuda_user_threads_test.cc
@@ -41,8 +41,7 @@
 #ifndef CERES_NO_CUDA
 #ifndef CERES_NO_THREADS
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
        DenseSchur_Cuda_UserOrdering_Threads) {  // NOLINT
@@ -60,8 +59,7 @@
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_NO_THREADS
 #endif  // CERES_NO_CUDA
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_denseschur_eigen_auto_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_denseschur_eigen_auto_test.cc
index 652b38f..d40276b 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_denseschur_eigen_auto_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_denseschur_eigen_auto_test.cc
@@ -38,8 +38,7 @@
 #include "ceres/internal/config.h"
 #include "bundle_adjustment_test_util.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
        DenseSchur_Eigen_AutomaticOrdering) {  // NOLINT
@@ -57,5 +56,4 @@
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_denseschur_eigen_auto_threads_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_denseschur_eigen_auto_threads_test.cc
index 476d4df..a355e85 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_denseschur_eigen_auto_threads_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_denseschur_eigen_auto_threads_test.cc
@@ -40,8 +40,7 @@
 
 #ifndef CERES_NO_THREADS
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
        DenseSchur_Eigen_AutomaticOrdering_Threads) {  // NOLINT
@@ -59,7 +58,6 @@
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_NO_THREADS
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_denseschur_eigen_user_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_denseschur_eigen_user_test.cc
index 8e6d673..0a9774d 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_denseschur_eigen_user_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_denseschur_eigen_user_test.cc
@@ -38,8 +38,7 @@
 #include "ceres/internal/config.h"
 #include "bundle_adjustment_test_util.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
        DenseSchur_Eigen_UserOrdering) {  // NOLINT
@@ -57,5 +56,4 @@
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_denseschur_eigen_user_threads_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_denseschur_eigen_user_threads_test.cc
index 7ac1494..f005c31 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_denseschur_eigen_user_threads_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_denseschur_eigen_user_threads_test.cc
@@ -40,8 +40,7 @@
 
 #ifndef CERES_NO_THREADS
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
        DenseSchur_Eigen_UserOrdering_Threads) {  // NOLINT
@@ -59,7 +58,6 @@
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_NO_THREADS
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_denseschur_lapack_auto_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_denseschur_lapack_auto_test.cc
index d43e9d2..c806593 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_denseschur_lapack_auto_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_denseschur_lapack_auto_test.cc
@@ -40,8 +40,7 @@
 
 #ifndef CERES_NO_LAPACK
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
        DenseSchur_Lapack_AutomaticOrdering) {  // NOLINT
@@ -59,7 +58,6 @@
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_NO_LAPACK
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_denseschur_lapack_auto_threads_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_denseschur_lapack_auto_threads_test.cc
index 6f5eada..4e727db 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_denseschur_lapack_auto_threads_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_denseschur_lapack_auto_threads_test.cc
@@ -41,8 +41,7 @@
 #ifndef CERES_NO_LAPACK
 #ifndef CERES_NO_THREADS
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
        DenseSchur_Lapack_AutomaticOrdering_Threads) {  // NOLINT
@@ -60,8 +59,7 @@
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_NO_THREADS
 #endif  // CERES_NO_LAPACK
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_denseschur_lapack_user_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_denseschur_lapack_user_test.cc
index 775746f..0c0b5ab 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_denseschur_lapack_user_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_denseschur_lapack_user_test.cc
@@ -40,8 +40,7 @@
 
 #ifndef CERES_NO_LAPACK
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
        DenseSchur_Lapack_UserOrdering) {  // NOLINT
@@ -59,7 +58,6 @@
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_NO_LAPACK
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_denseschur_lapack_user_threads_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_denseschur_lapack_user_threads_test.cc
index 050748d..e19734a 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_denseschur_lapack_user_threads_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_denseschur_lapack_user_threads_test.cc
@@ -41,8 +41,7 @@
 #ifndef CERES_NO_LAPACK
 #ifndef CERES_NO_THREADS
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
        DenseSchur_Lapack_UserOrdering_Threads) {  // NOLINT
@@ -60,8 +59,7 @@
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_NO_THREADS
 #endif  // CERES_NO_LAPACK
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_acceleratesparse_clustjacobi_auto_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_acceleratesparse_clustjacobi_auto_test.cc
index eb5f010..ad34ebe 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_acceleratesparse_clustjacobi_auto_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_acceleratesparse_clustjacobi_auto_test.cc
@@ -40,8 +40,7 @@
 
 #ifndef CERES_NO_ACCELERATE_SPARSE
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
        IterativeSchur_AccelerateSparse_ClusterJacobi_AutomaticOrdering) {  // NOLINT
@@ -59,7 +58,6 @@
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_NO_ACCELERATE_SPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_acceleratesparse_clustjacobi_auto_threads_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_acceleratesparse_clustjacobi_auto_threads_test.cc
index 58ba781..93b58eb 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_acceleratesparse_clustjacobi_auto_threads_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_acceleratesparse_clustjacobi_auto_threads_test.cc
@@ -41,8 +41,7 @@
 #ifndef CERES_NO_ACCELERATE_SPARSE
 #ifndef CERES_NO_THREADS
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
        IterativeSchur_AccelerateSparse_ClusterJacobi_AutomaticOrdering_Threads) {  // NOLINT
@@ -60,8 +59,7 @@
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_NO_THREADS
 #endif  // CERES_NO_ACCELERATE_SPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_acceleratesparse_clustjacobi_user_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_acceleratesparse_clustjacobi_user_test.cc
index a70f6e1..b1128c7 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_acceleratesparse_clustjacobi_user_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_acceleratesparse_clustjacobi_user_test.cc
@@ -40,8 +40,7 @@
 
 #ifndef CERES_NO_ACCELERATE_SPARSE
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
        IterativeSchur_AccelerateSparse_ClusterJacobi_UserOrdering) {  // NOLINT
@@ -59,7 +58,6 @@
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_NO_ACCELERATE_SPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_acceleratesparse_clustjacobi_user_threads_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_acceleratesparse_clustjacobi_user_threads_test.cc
index cc342a7..053e9b2 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_acceleratesparse_clustjacobi_user_threads_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_acceleratesparse_clustjacobi_user_threads_test.cc
@@ -41,8 +41,7 @@
 #ifndef CERES_NO_ACCELERATE_SPARSE
 #ifndef CERES_NO_THREADS
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
        IterativeSchur_AccelerateSparse_ClusterJacobi_UserOrdering_Threads) {  // NOLINT
@@ -60,8 +59,7 @@
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_NO_THREADS
 #endif  // CERES_NO_ACCELERATE_SPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_acceleratesparse_clusttri_auto_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_acceleratesparse_clusttri_auto_test.cc
index 09774cc..6a57a3d 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_acceleratesparse_clusttri_auto_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_acceleratesparse_clusttri_auto_test.cc
@@ -40,8 +40,7 @@
 
 #ifndef CERES_NO_ACCELERATE_SPARSE
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
        IterativeSchur_AccelerateSparse_ClusterTridiagonal_AutomaticOrdering) {  // NOLINT
@@ -59,7 +58,6 @@
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_NO_ACCELERATE_SPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_acceleratesparse_clusttri_auto_threads_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_acceleratesparse_clusttri_auto_threads_test.cc
index d33f4af..723246a 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_acceleratesparse_clusttri_auto_threads_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_acceleratesparse_clusttri_auto_threads_test.cc
@@ -41,8 +41,7 @@
 #ifndef CERES_NO_ACCELERATE_SPARSE
 #ifndef CERES_NO_THREADS
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
        IterativeSchur_AccelerateSparse_ClusterTridiagonal_AutomaticOrdering_Threads) {  // NOLINT
@@ -60,8 +59,7 @@
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_NO_THREADS
 #endif  // CERES_NO_ACCELERATE_SPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_acceleratesparse_clusttri_user_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_acceleratesparse_clusttri_user_test.cc
index 1452f9a..f3066c9 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_acceleratesparse_clusttri_user_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_acceleratesparse_clusttri_user_test.cc
@@ -40,8 +40,7 @@
 
 #ifndef CERES_NO_ACCELERATE_SPARSE
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
        IterativeSchur_AccelerateSparse_ClusterTridiagonal_UserOrdering) {  // NOLINT
@@ -59,7 +58,6 @@
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_NO_ACCELERATE_SPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_acceleratesparse_clusttri_user_threads_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_acceleratesparse_clusttri_user_threads_test.cc
index a784dd0..93f5353 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_acceleratesparse_clusttri_user_threads_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_acceleratesparse_clusttri_user_threads_test.cc
@@ -41,8 +41,7 @@
 #ifndef CERES_NO_ACCELERATE_SPARSE
 #ifndef CERES_NO_THREADS
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
        IterativeSchur_AccelerateSparse_ClusterTridiagonal_UserOrdering_Threads) {  // NOLINT
@@ -60,8 +59,7 @@
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_NO_THREADS
 #endif  // CERES_NO_ACCELERATE_SPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_cxsparse_clustjacobi_auto_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_cxsparse_clustjacobi_auto_test.cc
index b69c995..dedff9c 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_cxsparse_clustjacobi_auto_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_cxsparse_clustjacobi_auto_test.cc
@@ -40,8 +40,7 @@
 
 #ifndef CERES_NO_CXSPARSE
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
        IterativeSchur_CxSparse_ClusterJacobi_AutomaticOrdering) {  // NOLINT
@@ -59,7 +58,6 @@
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_NO_CXSPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_cxsparse_clustjacobi_auto_threads_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_cxsparse_clustjacobi_auto_threads_test.cc
index 814240e..3bcb11d 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_cxsparse_clustjacobi_auto_threads_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_cxsparse_clustjacobi_auto_threads_test.cc
@@ -41,8 +41,7 @@
 #ifndef CERES_NO_CXSPARSE
 #ifndef CERES_NO_THREADS
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
        IterativeSchur_CxSparse_ClusterJacobi_AutomaticOrdering_Threads) {  // NOLINT
@@ -60,8 +59,7 @@
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_NO_THREADS
 #endif  // CERES_NO_CXSPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_cxsparse_clustjacobi_user_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_cxsparse_clustjacobi_user_test.cc
index 0a912d5..5acbc66 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_cxsparse_clustjacobi_user_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_cxsparse_clustjacobi_user_test.cc
@@ -40,8 +40,7 @@
 
 #ifndef CERES_NO_CXSPARSE
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
        IterativeSchur_CxSparse_ClusterJacobi_UserOrdering) {  // NOLINT
@@ -59,7 +58,6 @@
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_NO_CXSPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_cxsparse_clustjacobi_user_threads_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_cxsparse_clustjacobi_user_threads_test.cc
index c404658..9e0baea 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_cxsparse_clustjacobi_user_threads_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_cxsparse_clustjacobi_user_threads_test.cc
@@ -41,8 +41,7 @@
 #ifndef CERES_NO_CXSPARSE
 #ifndef CERES_NO_THREADS
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
        IterativeSchur_CxSparse_ClusterJacobi_UserOrdering_Threads) {  // NOLINT
@@ -60,8 +59,7 @@
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_NO_THREADS
 #endif  // CERES_NO_CXSPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_cxsparse_clusttri_auto_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_cxsparse_clusttri_auto_test.cc
index 5350851..5e5c2ab 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_cxsparse_clusttri_auto_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_cxsparse_clusttri_auto_test.cc
@@ -40,8 +40,7 @@
 
 #ifndef CERES_NO_CXSPARSE
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
        IterativeSchur_CxSparse_ClusterTridiagonal_AutomaticOrdering) {  // NOLINT
@@ -59,7 +58,6 @@
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_NO_CXSPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_cxsparse_clusttri_auto_threads_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_cxsparse_clusttri_auto_threads_test.cc
index e84143a..d9d9fff 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_cxsparse_clusttri_auto_threads_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_cxsparse_clusttri_auto_threads_test.cc
@@ -41,8 +41,7 @@
 #ifndef CERES_NO_CXSPARSE
 #ifndef CERES_NO_THREADS
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
        IterativeSchur_CxSparse_ClusterTridiagonal_AutomaticOrdering_Threads) {  // NOLINT
@@ -60,8 +59,7 @@
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_NO_THREADS
 #endif  // CERES_NO_CXSPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_cxsparse_clusttri_user_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_cxsparse_clusttri_user_test.cc
index de32e05..b3176d0 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_cxsparse_clusttri_user_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_cxsparse_clusttri_user_test.cc
@@ -40,8 +40,7 @@
 
 #ifndef CERES_NO_CXSPARSE
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
        IterativeSchur_CxSparse_ClusterTridiagonal_UserOrdering) {  // NOLINT
@@ -59,7 +58,6 @@
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_NO_CXSPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_cxsparse_clusttri_user_threads_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_cxsparse_clusttri_user_threads_test.cc
index cef3f52..1922835 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_cxsparse_clusttri_user_threads_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_cxsparse_clusttri_user_threads_test.cc
@@ -41,8 +41,7 @@
 #ifndef CERES_NO_CXSPARSE
 #ifndef CERES_NO_THREADS
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
        IterativeSchur_CxSparse_ClusterTridiagonal_UserOrdering_Threads) {  // NOLINT
@@ -60,8 +59,7 @@
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_NO_THREADS
 #endif  // CERES_NO_CXSPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_eigensparse_clustjacobi_auto_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_eigensparse_clustjacobi_auto_test.cc
index fc5fb22..202d77a 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_eigensparse_clustjacobi_auto_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_eigensparse_clustjacobi_auto_test.cc
@@ -40,8 +40,7 @@
 
 #ifdef CERES_USE_EIGEN_SPARSE
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
        IterativeSchur_EigenSparse_ClusterJacobi_AutomaticOrdering) {  // NOLINT
@@ -59,7 +58,6 @@
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_USE_EIGEN_SPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_eigensparse_clustjacobi_auto_threads_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_eigensparse_clustjacobi_auto_threads_test.cc
index 588cde0..1e9dbf0 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_eigensparse_clustjacobi_auto_threads_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_eigensparse_clustjacobi_auto_threads_test.cc
@@ -41,8 +41,7 @@
 #ifdef CERES_USE_EIGEN_SPARSE
 #ifndef CERES_NO_THREADS
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
        IterativeSchur_EigenSparse_ClusterJacobi_AutomaticOrdering_Threads) {  // NOLINT
@@ -60,8 +59,7 @@
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_NO_THREADS
 #endif  // CERES_USE_EIGEN_SPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_eigensparse_clustjacobi_user_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_eigensparse_clustjacobi_user_test.cc
index c24cbe3..81f9a8b 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_eigensparse_clustjacobi_user_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_eigensparse_clustjacobi_user_test.cc
@@ -40,8 +40,7 @@
 
 #ifdef CERES_USE_EIGEN_SPARSE
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
        IterativeSchur_EigenSparse_ClusterJacobi_UserOrdering) {  // NOLINT
@@ -59,7 +58,6 @@
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_USE_EIGEN_SPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_eigensparse_clustjacobi_user_threads_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_eigensparse_clustjacobi_user_threads_test.cc
index 3407e90..0daf519 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_eigensparse_clustjacobi_user_threads_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_eigensparse_clustjacobi_user_threads_test.cc
@@ -41,8 +41,7 @@
 #ifdef CERES_USE_EIGEN_SPARSE
 #ifndef CERES_NO_THREADS
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
        IterativeSchur_EigenSparse_ClusterJacobi_UserOrdering_Threads) {  // NOLINT
@@ -60,8 +59,7 @@
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_NO_THREADS
 #endif  // CERES_USE_EIGEN_SPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_eigensparse_clusttri_auto_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_eigensparse_clusttri_auto_test.cc
index 93dc789..1667abe 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_eigensparse_clusttri_auto_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_eigensparse_clusttri_auto_test.cc
@@ -40,8 +40,7 @@
 
 #ifdef CERES_USE_EIGEN_SPARSE
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
        IterativeSchur_EigenSparse_ClusterTridiagonal_AutomaticOrdering) {  // NOLINT
@@ -59,7 +58,6 @@
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_USE_EIGEN_SPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_eigensparse_clusttri_auto_threads_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_eigensparse_clusttri_auto_threads_test.cc
index a1a503e..1ee1286 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_eigensparse_clusttri_auto_threads_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_eigensparse_clusttri_auto_threads_test.cc
@@ -41,8 +41,7 @@
 #ifdef CERES_USE_EIGEN_SPARSE
 #ifndef CERES_NO_THREADS
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
        IterativeSchur_EigenSparse_ClusterTridiagonal_AutomaticOrdering_Threads) {  // NOLINT
@@ -60,8 +59,7 @@
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_NO_THREADS
 #endif  // CERES_USE_EIGEN_SPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_eigensparse_clusttri_user_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_eigensparse_clusttri_user_test.cc
index 67bbe89..5bfb1b2 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_eigensparse_clusttri_user_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_eigensparse_clusttri_user_test.cc
@@ -40,8 +40,7 @@
 
 #ifdef CERES_USE_EIGEN_SPARSE
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
        IterativeSchur_EigenSparse_ClusterTridiagonal_UserOrdering) {  // NOLINT
@@ -59,7 +58,6 @@
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_USE_EIGEN_SPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_eigensparse_clusttri_user_threads_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_eigensparse_clusttri_user_threads_test.cc
index 21712b5..6e08b22 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_eigensparse_clusttri_user_threads_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_eigensparse_clusttri_user_threads_test.cc
@@ -41,8 +41,7 @@
 #ifdef CERES_USE_EIGEN_SPARSE
 #ifndef CERES_NO_THREADS
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
        IterativeSchur_EigenSparse_ClusterTridiagonal_UserOrdering_Threads) {  // NOLINT
@@ -60,8 +59,7 @@
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_NO_THREADS
 #endif  // CERES_USE_EIGEN_SPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_jacobi_auto_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_jacobi_auto_test.cc
index 2ed518f..81bb780 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_jacobi_auto_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_jacobi_auto_test.cc
@@ -38,8 +38,7 @@
 #include "ceres/internal/config.h"
 #include "bundle_adjustment_test_util.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
        IterativeSchur_Jacobi_AutomaticOrdering) {  // NOLINT
@@ -57,5 +56,4 @@
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_jacobi_auto_threads_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_jacobi_auto_threads_test.cc
index c0ce06b..e0aad44 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_jacobi_auto_threads_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_jacobi_auto_threads_test.cc
@@ -40,8 +40,7 @@
 
 #ifndef CERES_NO_THREADS
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
        IterativeSchur_Jacobi_AutomaticOrdering_Threads) {  // NOLINT
@@ -59,7 +58,6 @@
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_NO_THREADS
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_jacobi_user_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_jacobi_user_test.cc
index b8f87dd..1a6a196 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_jacobi_user_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_jacobi_user_test.cc
@@ -38,8 +38,7 @@
 #include "ceres/internal/config.h"
 #include "bundle_adjustment_test_util.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
        IterativeSchur_Jacobi_UserOrdering) {  // NOLINT
@@ -57,5 +56,4 @@
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_jacobi_user_threads_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_jacobi_user_threads_test.cc
index 34469ff..c68f6f0 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_jacobi_user_threads_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_jacobi_user_threads_test.cc
@@ -40,8 +40,7 @@
 
 #ifndef CERES_NO_THREADS
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
        IterativeSchur_Jacobi_UserOrdering_Threads) {  // NOLINT
@@ -59,7 +58,6 @@
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_NO_THREADS
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_schurjacobi_auto_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_schurjacobi_auto_test.cc
index b6eb469..a99ad57 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_schurjacobi_auto_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_schurjacobi_auto_test.cc
@@ -38,8 +38,7 @@
 #include "ceres/internal/config.h"
 #include "bundle_adjustment_test_util.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
        IterativeSchur_SchurJacobi_AutomaticOrdering) {  // NOLINT
@@ -57,5 +56,4 @@
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_schurjacobi_auto_threads_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_schurjacobi_auto_threads_test.cc
index 033c7ce..6d97eba 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_schurjacobi_auto_threads_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_schurjacobi_auto_threads_test.cc
@@ -40,8 +40,7 @@
 
 #ifndef CERES_NO_THREADS
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
        IterativeSchur_SchurJacobi_AutomaticOrdering_Threads) {  // NOLINT
@@ -59,7 +58,6 @@
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_NO_THREADS
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_schurjacobi_user_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_schurjacobi_user_test.cc
index 127c64b..8b77504 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_schurjacobi_user_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_schurjacobi_user_test.cc
@@ -38,8 +38,7 @@
 #include "ceres/internal/config.h"
 #include "bundle_adjustment_test_util.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
        IterativeSchur_SchurJacobi_UserOrdering) {  // NOLINT
@@ -57,5 +56,4 @@
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_schurjacobi_user_threads_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_schurjacobi_user_threads_test.cc
index 8a72df7..71220f7 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_schurjacobi_user_threads_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_schurjacobi_user_threads_test.cc
@@ -40,8 +40,7 @@
 
 #ifndef CERES_NO_THREADS
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
        IterativeSchur_SchurJacobi_UserOrdering_Threads) {  // NOLINT
@@ -59,7 +58,6 @@
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_NO_THREADS
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_suitesparse_clustjacobi_auto_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_suitesparse_clustjacobi_auto_test.cc
index 545d980..d5ffb32 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_suitesparse_clustjacobi_auto_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_suitesparse_clustjacobi_auto_test.cc
@@ -40,8 +40,7 @@
 
 #ifndef CERES_NO_SUITESPARSE
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
        IterativeSchur_SuiteSparse_ClusterJacobi_AutomaticOrdering) {  // NOLINT
@@ -59,7 +58,6 @@
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_NO_SUITESPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_suitesparse_clustjacobi_auto_threads_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_suitesparse_clustjacobi_auto_threads_test.cc
index 2cbcd34..874168d 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_suitesparse_clustjacobi_auto_threads_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_suitesparse_clustjacobi_auto_threads_test.cc
@@ -41,8 +41,7 @@
 #ifndef CERES_NO_SUITESPARSE
 #ifndef CERES_NO_THREADS
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
        IterativeSchur_SuiteSparse_ClusterJacobi_AutomaticOrdering_Threads) {  // NOLINT
@@ -60,8 +59,7 @@
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_NO_THREADS
 #endif  // CERES_NO_SUITESPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_suitesparse_clustjacobi_user_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_suitesparse_clustjacobi_user_test.cc
index c41f2ce..a16665d 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_suitesparse_clustjacobi_user_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_suitesparse_clustjacobi_user_test.cc
@@ -40,8 +40,7 @@
 
 #ifndef CERES_NO_SUITESPARSE
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
        IterativeSchur_SuiteSparse_ClusterJacobi_UserOrdering) {  // NOLINT
@@ -59,7 +58,6 @@
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_NO_SUITESPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_suitesparse_clustjacobi_user_threads_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_suitesparse_clustjacobi_user_threads_test.cc
index 31d8f3f..ae07667 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_suitesparse_clustjacobi_user_threads_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_suitesparse_clustjacobi_user_threads_test.cc
@@ -41,8 +41,7 @@
 #ifndef CERES_NO_SUITESPARSE
 #ifndef CERES_NO_THREADS
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
        IterativeSchur_SuiteSparse_ClusterJacobi_UserOrdering_Threads) {  // NOLINT
@@ -60,8 +59,7 @@
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_NO_THREADS
 #endif  // CERES_NO_SUITESPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_suitesparse_clusttri_auto_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_suitesparse_clusttri_auto_test.cc
index 3989211..bfc7ec6 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_suitesparse_clusttri_auto_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_suitesparse_clusttri_auto_test.cc
@@ -40,8 +40,7 @@
 
 #ifndef CERES_NO_SUITESPARSE
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
        IterativeSchur_SuiteSparse_ClusterTridiagonal_AutomaticOrdering) {  // NOLINT
@@ -59,7 +58,6 @@
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_NO_SUITESPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_suitesparse_clusttri_auto_threads_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_suitesparse_clusttri_auto_threads_test.cc
index 3b35478..aee5e5a 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_suitesparse_clusttri_auto_threads_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_suitesparse_clusttri_auto_threads_test.cc
@@ -41,8 +41,7 @@
 #ifndef CERES_NO_SUITESPARSE
 #ifndef CERES_NO_THREADS
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
        IterativeSchur_SuiteSparse_ClusterTridiagonal_AutomaticOrdering_Threads) {  // NOLINT
@@ -60,8 +59,7 @@
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_NO_THREADS
 #endif  // CERES_NO_SUITESPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_suitesparse_clusttri_user_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_suitesparse_clusttri_user_test.cc
index ca0efe9..9789b3e 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_suitesparse_clusttri_user_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_suitesparse_clusttri_user_test.cc
@@ -40,8 +40,7 @@
 
 #ifndef CERES_NO_SUITESPARSE
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
        IterativeSchur_SuiteSparse_ClusterTridiagonal_UserOrdering) {  // NOLINT
@@ -59,7 +58,6 @@
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_NO_SUITESPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_suitesparse_clusttri_user_threads_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_suitesparse_clusttri_user_threads_test.cc
index d9fc093..9bc2d3f 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_suitesparse_clusttri_user_threads_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_iterschur_suitesparse_clusttri_user_threads_test.cc
@@ -41,8 +41,7 @@
 #ifndef CERES_NO_SUITESPARSE
 #ifndef CERES_NO_THREADS
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
        IterativeSchur_SuiteSparse_ClusterTridiagonal_UserOrdering_Threads) {  // NOLINT
@@ -60,8 +59,7 @@
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_NO_THREADS
 #endif  // CERES_NO_SUITESPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_acceleratesparse_auto_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_acceleratesparse_auto_test.cc
index 46c5e06..b735073 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_acceleratesparse_auto_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_acceleratesparse_auto_test.cc
@@ -40,8 +40,7 @@
 
 #ifndef CERES_NO_ACCELERATE_SPARSE
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
        SparseNormalCholesky_AccelerateSparse_AutomaticOrdering) {  // NOLINT
@@ -59,7 +58,6 @@
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_NO_ACCELERATE_SPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_acceleratesparse_auto_threads_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_acceleratesparse_auto_threads_test.cc
index 7645695..79769b4 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_acceleratesparse_auto_threads_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_acceleratesparse_auto_threads_test.cc
@@ -41,8 +41,7 @@
 #ifndef CERES_NO_ACCELERATE_SPARSE
 #ifndef CERES_NO_THREADS
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
        SparseNormalCholesky_AccelerateSparse_AutomaticOrdering_Threads) {  // NOLINT
@@ -60,8 +59,7 @@
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_NO_THREADS
 #endif  // CERES_NO_ACCELERATE_SPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_acceleratesparse_user_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_acceleratesparse_user_test.cc
index 5f29691..286ad67 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_acceleratesparse_user_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_acceleratesparse_user_test.cc
@@ -40,8 +40,7 @@
 
 #ifndef CERES_NO_ACCELERATE_SPARSE
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
        SparseNormalCholesky_AccelerateSparse_UserOrdering) {  // NOLINT
@@ -59,7 +58,6 @@
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_NO_ACCELERATE_SPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_acceleratesparse_user_threads_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_acceleratesparse_user_threads_test.cc
index f40e8aa..6131f1d 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_acceleratesparse_user_threads_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_acceleratesparse_user_threads_test.cc
@@ -41,8 +41,7 @@
 #ifndef CERES_NO_ACCELERATE_SPARSE
 #ifndef CERES_NO_THREADS
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
        SparseNormalCholesky_AccelerateSparse_UserOrdering_Threads) {  // NOLINT
@@ -60,8 +59,7 @@
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_NO_THREADS
 #endif  // CERES_NO_ACCELERATE_SPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_cxsparse_auto_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_cxsparse_auto_test.cc
index 1c6c07d..17b96296 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_cxsparse_auto_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_cxsparse_auto_test.cc
@@ -40,8 +40,7 @@
 
 #ifndef CERES_NO_CXSPARSE
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
        SparseNormalCholesky_CxSparse_AutomaticOrdering) {  // NOLINT
@@ -59,7 +58,6 @@
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_NO_CXSPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_cxsparse_auto_threads_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_cxsparse_auto_threads_test.cc
index 76ce13d..bd454ac 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_cxsparse_auto_threads_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_cxsparse_auto_threads_test.cc
@@ -41,8 +41,7 @@
 #ifndef CERES_NO_CXSPARSE
 #ifndef CERES_NO_THREADS
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
        SparseNormalCholesky_CxSparse_AutomaticOrdering_Threads) {  // NOLINT
@@ -60,8 +59,7 @@
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_NO_THREADS
 #endif  // CERES_NO_CXSPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_cxsparse_user_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_cxsparse_user_test.cc
index a34b617..f071f57 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_cxsparse_user_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_cxsparse_user_test.cc
@@ -40,8 +40,7 @@
 
 #ifndef CERES_NO_CXSPARSE
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
        SparseNormalCholesky_CxSparse_UserOrdering) {  // NOLINT
@@ -59,7 +58,6 @@
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_NO_CXSPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_cxsparse_user_threads_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_cxsparse_user_threads_test.cc
index 0a9935a..129247b 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_cxsparse_user_threads_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_cxsparse_user_threads_test.cc
@@ -41,8 +41,7 @@
 #ifndef CERES_NO_CXSPARSE
 #ifndef CERES_NO_THREADS
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
        SparseNormalCholesky_CxSparse_UserOrdering_Threads) {  // NOLINT
@@ -60,8 +59,7 @@
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_NO_THREADS
 #endif  // CERES_NO_CXSPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_eigensparse_auto_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_eigensparse_auto_test.cc
index 6f6905b..268d760 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_eigensparse_auto_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_eigensparse_auto_test.cc
@@ -40,8 +40,7 @@
 
 #ifdef CERES_USE_EIGEN_SPARSE
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
        SparseNormalCholesky_EigenSparse_AutomaticOrdering) {  // NOLINT
@@ -59,7 +58,6 @@
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_USE_EIGEN_SPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_eigensparse_auto_threads_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_eigensparse_auto_threads_test.cc
index 6bd90e1..46e5dac 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_eigensparse_auto_threads_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_eigensparse_auto_threads_test.cc
@@ -41,8 +41,7 @@
 #ifdef CERES_USE_EIGEN_SPARSE
 #ifndef CERES_NO_THREADS
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
        SparseNormalCholesky_EigenSparse_AutomaticOrdering_Threads) {  // NOLINT
@@ -60,8 +59,7 @@
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_NO_THREADS
 #endif  // CERES_USE_EIGEN_SPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_eigensparse_user_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_eigensparse_user_test.cc
index bd32cd0..7f4f356 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_eigensparse_user_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_eigensparse_user_test.cc
@@ -40,8 +40,7 @@
 
 #ifdef CERES_USE_EIGEN_SPARSE
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
        SparseNormalCholesky_EigenSparse_UserOrdering) {  // NOLINT
@@ -59,7 +58,6 @@
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_USE_EIGEN_SPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_eigensparse_user_threads_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_eigensparse_user_threads_test.cc
index ff3adb8..68f3be7 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_eigensparse_user_threads_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_eigensparse_user_threads_test.cc
@@ -41,8 +41,7 @@
 #ifdef CERES_USE_EIGEN_SPARSE
 #ifndef CERES_NO_THREADS
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
        SparseNormalCholesky_EigenSparse_UserOrdering_Threads) {  // NOLINT
@@ -60,8 +59,7 @@
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_NO_THREADS
 #endif  // CERES_USE_EIGEN_SPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_suitesparse_auto_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_suitesparse_auto_test.cc
index a3b40c6..ef7f8fc 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_suitesparse_auto_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_suitesparse_auto_test.cc
@@ -40,8 +40,7 @@
 
 #ifndef CERES_NO_SUITESPARSE
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
        SparseNormalCholesky_SuiteSparse_AutomaticOrdering) {  // NOLINT
@@ -59,7 +58,6 @@
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_NO_SUITESPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_suitesparse_auto_threads_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_suitesparse_auto_threads_test.cc
index 496e447..ef11005 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_suitesparse_auto_threads_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_suitesparse_auto_threads_test.cc
@@ -41,8 +41,7 @@
 #ifndef CERES_NO_SUITESPARSE
 #ifndef CERES_NO_THREADS
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
        SparseNormalCholesky_SuiteSparse_AutomaticOrdering_Threads) {  // NOLINT
@@ -60,8 +59,7 @@
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_NO_THREADS
 #endif  // CERES_NO_SUITESPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_suitesparse_user_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_suitesparse_user_test.cc
index 11964a4..86b8322 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_suitesparse_user_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_suitesparse_user_test.cc
@@ -40,8 +40,7 @@
 
 #ifndef CERES_NO_SUITESPARSE
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
        SparseNormalCholesky_SuiteSparse_UserOrdering) {  // NOLINT
@@ -59,7 +58,6 @@
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_NO_SUITESPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_suitesparse_user_threads_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_suitesparse_user_threads_test.cc
index f41a173..862142a 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_suitesparse_user_threads_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_sparsecholesky_suitesparse_user_threads_test.cc
@@ -41,8 +41,7 @@
 #ifndef CERES_NO_SUITESPARSE
 #ifndef CERES_NO_THREADS
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
        SparseNormalCholesky_SuiteSparse_UserOrdering_Threads) {  // NOLINT
@@ -60,8 +59,7 @@
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_NO_THREADS
 #endif  // CERES_NO_SUITESPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_acceleratesparse_auto_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_acceleratesparse_auto_test.cc
index 905493b..c28727c 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_acceleratesparse_auto_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_acceleratesparse_auto_test.cc
@@ -40,8 +40,7 @@
 
 #ifndef CERES_NO_ACCELERATE_SPARSE
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
        SparseSchur_AccelerateSparse_AutomaticOrdering) {  // NOLINT
@@ -59,7 +58,6 @@
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_NO_ACCELERATE_SPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_acceleratesparse_auto_threads_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_acceleratesparse_auto_threads_test.cc
index 4071b03..595fc15 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_acceleratesparse_auto_threads_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_acceleratesparse_auto_threads_test.cc
@@ -41,8 +41,7 @@
 #ifndef CERES_NO_ACCELERATE_SPARSE
 #ifndef CERES_NO_THREADS
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
        SparseSchur_AccelerateSparse_AutomaticOrdering_Threads) {  // NOLINT
@@ -60,8 +59,7 @@
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_NO_THREADS
 #endif  // CERES_NO_ACCELERATE_SPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_acceleratesparse_user_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_acceleratesparse_user_test.cc
index 1829948..0d4cab1 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_acceleratesparse_user_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_acceleratesparse_user_test.cc
@@ -40,8 +40,7 @@
 
 #ifndef CERES_NO_ACCELERATE_SPARSE
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
        SparseSchur_AccelerateSparse_UserOrdering) {  // NOLINT
@@ -59,7 +58,6 @@
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_NO_ACCELERATE_SPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_acceleratesparse_user_threads_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_acceleratesparse_user_threads_test.cc
index 531045e..c1302f7 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_acceleratesparse_user_threads_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_acceleratesparse_user_threads_test.cc
@@ -41,8 +41,7 @@
 #ifndef CERES_NO_ACCELERATE_SPARSE
 #ifndef CERES_NO_THREADS
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
        SparseSchur_AccelerateSparse_UserOrdering_Threads) {  // NOLINT
@@ -60,8 +59,7 @@
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_NO_THREADS
 #endif  // CERES_NO_ACCELERATE_SPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_cxsparse_auto_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_cxsparse_auto_test.cc
index b2f2077..22bed0e 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_cxsparse_auto_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_cxsparse_auto_test.cc
@@ -40,8 +40,7 @@
 
 #ifndef CERES_NO_CXSPARSE
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
        SparseSchur_CxSparse_AutomaticOrdering) {  // NOLINT
@@ -59,7 +58,6 @@
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_NO_CXSPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_cxsparse_auto_threads_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_cxsparse_auto_threads_test.cc
index 98f19d6..53d06c6 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_cxsparse_auto_threads_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_cxsparse_auto_threads_test.cc
@@ -41,8 +41,7 @@
 #ifndef CERES_NO_CXSPARSE
 #ifndef CERES_NO_THREADS
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
        SparseSchur_CxSparse_AutomaticOrdering_Threads) {  // NOLINT
@@ -60,8 +59,7 @@
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_NO_THREADS
 #endif  // CERES_NO_CXSPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_cxsparse_user_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_cxsparse_user_test.cc
index 03ce57d..0f4d00a 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_cxsparse_user_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_cxsparse_user_test.cc
@@ -40,8 +40,7 @@
 
 #ifndef CERES_NO_CXSPARSE
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
        SparseSchur_CxSparse_UserOrdering) {  // NOLINT
@@ -59,7 +58,6 @@
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_NO_CXSPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_cxsparse_user_threads_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_cxsparse_user_threads_test.cc
index fd14b3d..49418c4 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_cxsparse_user_threads_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_cxsparse_user_threads_test.cc
@@ -41,8 +41,7 @@
 #ifndef CERES_NO_CXSPARSE
 #ifndef CERES_NO_THREADS
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
        SparseSchur_CxSparse_UserOrdering_Threads) {  // NOLINT
@@ -60,8 +59,7 @@
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_NO_THREADS
 #endif  // CERES_NO_CXSPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_eigensparse_auto_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_eigensparse_auto_test.cc
index 140ca13..65790a7 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_eigensparse_auto_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_eigensparse_auto_test.cc
@@ -40,8 +40,7 @@
 
 #ifdef CERES_USE_EIGEN_SPARSE
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
        SparseSchur_EigenSparse_AutomaticOrdering) {  // NOLINT
@@ -59,7 +58,6 @@
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_USE_EIGEN_SPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_eigensparse_auto_threads_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_eigensparse_auto_threads_test.cc
index fc8197f..137725b 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_eigensparse_auto_threads_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_eigensparse_auto_threads_test.cc
@@ -41,8 +41,7 @@
 #ifdef CERES_USE_EIGEN_SPARSE
 #ifndef CERES_NO_THREADS
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
        SparseSchur_EigenSparse_AutomaticOrdering_Threads) {  // NOLINT
@@ -60,8 +59,7 @@
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_NO_THREADS
 #endif  // CERES_USE_EIGEN_SPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_eigensparse_user_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_eigensparse_user_test.cc
index 894b4ac..38e50ad 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_eigensparse_user_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_eigensparse_user_test.cc
@@ -40,8 +40,7 @@
 
 #ifdef CERES_USE_EIGEN_SPARSE
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
        SparseSchur_EigenSparse_UserOrdering) {  // NOLINT
@@ -59,7 +58,6 @@
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_USE_EIGEN_SPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_eigensparse_user_threads_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_eigensparse_user_threads_test.cc
index 5bc7599..14dcabf 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_eigensparse_user_threads_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_eigensparse_user_threads_test.cc
@@ -41,8 +41,7 @@
 #ifdef CERES_USE_EIGEN_SPARSE
 #ifndef CERES_NO_THREADS
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
        SparseSchur_EigenSparse_UserOrdering_Threads) {  // NOLINT
@@ -60,8 +59,7 @@
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_NO_THREADS
 #endif  // CERES_USE_EIGEN_SPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_suitesparse_auto_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_suitesparse_auto_test.cc
index 3d89edb..3596ae1 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_suitesparse_auto_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_suitesparse_auto_test.cc
@@ -40,8 +40,7 @@
 
 #ifndef CERES_NO_SUITESPARSE
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
        SparseSchur_SuiteSparse_AutomaticOrdering) {  // NOLINT
@@ -59,7 +58,6 @@
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_NO_SUITESPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_suitesparse_auto_threads_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_suitesparse_auto_threads_test.cc
index 2858545..cf015b8 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_suitesparse_auto_threads_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_suitesparse_auto_threads_test.cc
@@ -41,8 +41,7 @@
 #ifndef CERES_NO_SUITESPARSE
 #ifndef CERES_NO_THREADS
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
        SparseSchur_SuiteSparse_AutomaticOrdering_Threads) {  // NOLINT
@@ -60,8 +59,7 @@
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_NO_THREADS
 #endif  // CERES_NO_SUITESPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_suitesparse_user_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_suitesparse_user_test.cc
index 542ba66..0c78bee 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_suitesparse_user_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_suitesparse_user_test.cc
@@ -40,8 +40,7 @@
 
 #ifndef CERES_NO_SUITESPARSE
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
        SparseSchur_SuiteSparse_UserOrdering) {  // NOLINT
@@ -59,7 +58,6 @@
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_NO_SUITESPARSE
diff --git a/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_suitesparse_user_threads_test.cc b/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_suitesparse_user_threads_test.cc
index 0925d16..b13915e 100644
--- a/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_suitesparse_user_threads_test.cc
+++ b/internal/ceres/generated_bundle_adjustment_tests/ba_sparseschur_suitesparse_user_threads_test.cc
@@ -41,8 +41,7 @@
 #ifndef CERES_NO_SUITESPARSE
 #ifndef CERES_NO_THREADS
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST_F(BundleAdjustmentTest,
        SparseSchur_SuiteSparse_UserOrdering_Threads) {  // NOLINT
@@ -60,8 +59,7 @@
   RunSolverForConfigAndExpectResidualsMatch(*options, problem);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_NO_THREADS
 #endif  // CERES_NO_SUITESPARSE
diff --git a/internal/ceres/gradient_checker_test.cc b/internal/ceres/gradient_checker_test.cc
index bef7668..208a0a7 100644
--- a/internal/ceres/gradient_checker_test.cc
+++ b/internal/ceres/gradient_checker_test.cc
@@ -45,8 +45,7 @@
 #include "glog/logging.h"
 #include "gtest/gtest.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 using std::vector;
 const double kTolerance = 1e-12;
@@ -832,5 +831,4 @@
   EXPECT_EQ(CONVERGENCE, summary.termination_type);
   EXPECT_LE(summary.final_cost, 1e-12);
 }
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/gradient_checking_cost_function.cc b/internal/ceres/gradient_checking_cost_function.cc
index 1c3b318..04440c2 100644
--- a/internal/ceres/gradient_checking_cost_function.cc
+++ b/internal/ceres/gradient_checking_cost_function.cc
@@ -52,8 +52,7 @@
 #include "ceres/types.h"
 #include "glog/logging.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 using std::abs;
 using std::max;
@@ -280,5 +279,4 @@
   return gradient_checking_problem_impl;
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/gradient_checking_cost_function.h b/internal/ceres/gradient_checking_cost_function.h
index 0caafaf..c88f9ad 100644
--- a/internal/ceres/gradient_checking_cost_function.h
+++ b/internal/ceres/gradient_checking_cost_function.h
@@ -42,8 +42,7 @@
 #include "ceres/iteration_callback.h"
 #include "ceres/manifold.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 class ProblemImpl;
 
@@ -109,8 +108,7 @@
     double relative_precision,
     GradientCheckingIterationCallback* callback);
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #include "ceres/internal/reenable_warnings.h"
 
diff --git a/internal/ceres/gradient_checking_cost_function_test.cc b/internal/ceres/gradient_checking_cost_function_test.cc
index 9994efa..ba5c013 100644
--- a/internal/ceres/gradient_checking_cost_function_test.cc
+++ b/internal/ceres/gradient_checking_cost_function_test.cc
@@ -50,8 +50,7 @@
 #include "gmock/gmock.h"
 #include "gtest/gtest.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 using std::vector;
 using testing::_;
@@ -526,5 +525,4 @@
   }
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/gradient_problem_evaluator.h b/internal/ceres/gradient_problem_evaluator.h
index efbb257..8f74289 100644
--- a/internal/ceres/gradient_problem_evaluator.h
+++ b/internal/ceres/gradient_problem_evaluator.h
@@ -43,8 +43,7 @@
 #include "ceres/sparse_matrix.h"
 #include "ceres/wall_time.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 class CERES_NO_EXPORT GradientProblemEvaluator final : public Evaluator {
  public:
@@ -97,8 +96,7 @@
   ::ceres::internal::ExecutionSummary execution_summary_;
 };
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #include "ceres/internal/reenable_warnings.h"
 
diff --git a/internal/ceres/gradient_problem_solver_test.cc b/internal/ceres/gradient_problem_solver_test.cc
index ffd827e..1ede243 100644
--- a/internal/ceres/gradient_problem_solver_test.cc
+++ b/internal/ceres/gradient_problem_solver_test.cc
@@ -33,8 +33,7 @@
 #include "ceres/gradient_problem.h"
 #include "gtest/gtest.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 // Rosenbrock function; see http://en.wikipedia.org/wiki/Rosenbrock_function .
 class Rosenbrock : public ceres::FirstOrderFunction {
@@ -127,5 +126,4 @@
   EXPECT_NE(original_x, callback.x_values[1]);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/gradient_problem_test.cc b/internal/ceres/gradient_problem_test.cc
index 47f4348..a3d18e7 100644
--- a/internal/ceres/gradient_problem_test.cc
+++ b/internal/ceres/gradient_problem_test.cc
@@ -32,8 +32,7 @@
 
 #include "gtest/gtest.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 class QuadraticTestFunction : public ceres::FirstOrderFunction {
  public:
@@ -133,5 +132,4 @@
   EXPECT_EQ(2.0 * x, gradient);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/graph.h b/internal/ceres/graph.h
index 6a6f8f0..acae8c2 100644
--- a/internal/ceres/graph.h
+++ b/internal/ceres/graph.h
@@ -42,8 +42,7 @@
 #include "ceres/types.h"
 #include "glog/logging.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 // A unweighted undirected graph templated over the vertex ids. Vertex
 // should be hashable.
@@ -206,7 +205,6 @@
       edge_weights_;
 };
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_INTERNAL_GRAPH_H_
diff --git a/internal/ceres/graph_algorithms.h b/internal/ceres/graph_algorithms.h
index 5299f80..ea4b177 100644
--- a/internal/ceres/graph_algorithms.h
+++ b/internal/ceres/graph_algorithms.h
@@ -45,8 +45,7 @@
 #include "ceres/wall_time.h"
 #include "glog/logging.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 // Compare two vertices of a graph by their degrees, if the degrees
 // are equal then order them by their ids.
@@ -340,7 +339,6 @@
   return forest;
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_INTERNAL_GRAPH_ALGORITHMS_H_
diff --git a/internal/ceres/graph_algorithms_test.cc b/internal/ceres/graph_algorithms_test.cc
index 59232db..c03cda4 100644
--- a/internal/ceres/graph_algorithms_test.cc
+++ b/internal/ceres/graph_algorithms_test.cc
@@ -38,8 +38,7 @@
 #include "ceres/internal/export.h"
 #include "gtest/gtest.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 using std::vector;
 
@@ -244,5 +243,4 @@
   }
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/graph_test.cc b/internal/ceres/graph_test.cc
index 2154a06..9abe0b7 100644
--- a/internal/ceres/graph_test.cc
+++ b/internal/ceres/graph_test.cc
@@ -34,8 +34,7 @@
 
 #include "gtest/gtest.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST(Graph, EmptyGraph) {
   Graph<int> graph;
@@ -148,5 +147,4 @@
   EXPECT_EQ(graph.EdgeWeight(2, 3), 0);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/householder_vector_test.cc b/internal/ceres/householder_vector_test.cc
index 6f3b172..f6b2e53 100644
--- a/internal/ceres/householder_vector_test.cc
+++ b/internal/ceres/householder_vector_test.cc
@@ -34,8 +34,7 @@
 #include "glog/logging.h"
 #include "gtest/gtest.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 static void HouseholderTestHelper(const Vector& x) {
   const double kTolerance = 1e-14;
@@ -116,5 +115,4 @@
   HouseholderTestHelper(x);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/implicit_schur_complement.cc b/internal/ceres/implicit_schur_complement.cc
index 677d767..7946a56 100644
--- a/internal/ceres/implicit_schur_complement.cc
+++ b/internal/ceres/implicit_schur_complement.cc
@@ -38,8 +38,7 @@
 #include "ceres/types.h"
 #include "glog/logging.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 ImplicitSchurComplement::ImplicitSchurComplement(
     const LinearSolver::Options& options)
@@ -212,5 +211,4 @@
   A_->LeftMultiplyF(tmp_rows_.data(), rhs_.data());
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/implicit_schur_complement.h b/internal/ceres/implicit_schur_complement.h
index 598d484..601f2e6 100644
--- a/internal/ceres/implicit_schur_complement.h
+++ b/internal/ceres/implicit_schur_complement.h
@@ -44,8 +44,7 @@
 #include "ceres/partitioned_matrix_view.h"
 #include "ceres/types.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 class BlockSparseMatrix;
 
@@ -163,8 +162,7 @@
   mutable Vector tmp_f_cols_;
 };
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #include "ceres/internal/reenable_warnings.h"
 
diff --git a/internal/ceres/implicit_schur_complement_test.cc b/internal/ceres/implicit_schur_complement_test.cc
index b4f618c..baa381a 100644
--- a/internal/ceres/implicit_schur_complement_test.cc
+++ b/internal/ceres/implicit_schur_complement_test.cc
@@ -47,8 +47,7 @@
 #include "glog/logging.h"
 #include "gtest/gtest.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 using testing::AssertionResult;
 
@@ -206,5 +205,4 @@
   EXPECT_TRUE(TestImplicitSchurComplement(D_.get()));
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/inner_product_computer.cc b/internal/ceres/inner_product_computer.cc
index fbc43bf..1500817 100644
--- a/internal/ceres/inner_product_computer.cc
+++ b/internal/ceres/inner_product_computer.cc
@@ -35,8 +35,7 @@
 
 #include "ceres/small_blas.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 // Create the CompressedRowSparseMatrix matrix that will contain the
 // inner product.
@@ -330,5 +329,4 @@
   CHECK_EQ(cursor, result_offsets_.size());
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/inner_product_computer.h b/internal/ceres/inner_product_computer.h
index c6ed0b2..029800b 100644
--- a/internal/ceres/inner_product_computer.h
+++ b/internal/ceres/inner_product_computer.h
@@ -39,8 +39,7 @@
 #include "ceres/internal/disable_warnings.h"
 #include "ceres/internal/export.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 // This class is used to repeatedly compute the inner product
 //
@@ -153,8 +152,7 @@
   std::vector<int> result_offsets_;
 };
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #include "ceres/internal/reenable_warnings.h"
 
diff --git a/internal/ceres/integer_sequence_algorithm_test.cc b/internal/ceres/integer_sequence_algorithm_test.cc
index 4622fea..d2b4144 100644
--- a/internal/ceres/integer_sequence_algorithm_test.cc
+++ b/internal/ceres/integer_sequence_algorithm_test.cc
@@ -36,8 +36,7 @@
 
 #include "ceres/internal/jet_traits.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 // Unit tests for exclusive scan of integer sequence.
 static_assert(std::is_same<ExclusiveScan<std::integer_sequence<int>>,
@@ -136,5 +135,4 @@
     IsEmptyOrAreAllEqual_v<std::integer_sequence<long, 111, 111, 111, 111>>,
     "expected all equal sequence is not");
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/invert_psd_matrix.h b/internal/ceres/invert_psd_matrix.h
index ac8808b..51cc824 100644
--- a/internal/ceres/invert_psd_matrix.h
+++ b/internal/ceres/invert_psd_matrix.h
@@ -35,8 +35,7 @@
 #include "ceres/internal/eigen.h"
 #include "glog/logging.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 // Helper routine to compute the inverse or pseudo-inverse of a
 // symmetric positive semi-definite matrix.
@@ -73,7 +72,6 @@
   return svd.solve(MType::Identity(size, size));
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_INTERNAL_INVERT_PSD_MATRIX_H_
diff --git a/internal/ceres/invert_psd_matrix_benchmark.cc b/internal/ceres/invert_psd_matrix_benchmark.cc
index a10484f..017d331 100644
--- a/internal/ceres/invert_psd_matrix_benchmark.cc
+++ b/internal/ceres/invert_psd_matrix_benchmark.cc
@@ -32,8 +32,7 @@
 #include "benchmark/benchmark.h"
 #include "ceres/invert_psd_matrix.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 template <int kSize>
 void BenchmarkFixedSizedInvertPSDMatrix(benchmark::State& state) {
@@ -84,7 +83,6 @@
       }
     });
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 BENCHMARK_MAIN();
diff --git a/internal/ceres/invert_psd_matrix_test.cc b/internal/ceres/invert_psd_matrix_test.cc
index 279eeab..6feba7b 100644
--- a/internal/ceres/invert_psd_matrix_test.cc
+++ b/internal/ceres/invert_psd_matrix_test.cc
@@ -33,8 +33,7 @@
 #include "ceres/internal/eigen.h"
 #include "gtest/gtest.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 static constexpr bool kFullRank = true;
 static constexpr bool kRankDeficient = false;
@@ -109,5 +108,4 @@
               10 * std::numeric_limits<double>::epsilon());
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/is_close.cc b/internal/ceres/is_close.cc
index 0becf55..14f2151 100644
--- a/internal/ceres/is_close.cc
+++ b/internal/ceres/is_close.cc
@@ -33,8 +33,7 @@
 #include <algorithm>
 #include <cmath>
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 bool IsClose(double x,
              double y,
              double relative_precision,
@@ -57,5 +56,4 @@
   }
   return *relative_error < std::fabs(relative_precision);
 }
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/is_close.h b/internal/ceres/is_close.h
index a1e4e2f..1b4e613 100644
--- a/internal/ceres/is_close.h
+++ b/internal/ceres/is_close.h
@@ -36,8 +36,7 @@
 #include "ceres/internal/disable_warnings.h"
 #include "ceres/internal/export.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 // Returns true if x and y have a relative (unsigned) difference less than
 // relative_precision and false otherwise. Stores the relative and absolute
 // difference in relative/absolute_error if non-nullptr. If one of the two
@@ -48,8 +47,7 @@
                              double relative_precision,
                              double* relative_error,
                              double* absolute_error);
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #include "ceres/internal/reenable_warnings.h"
 
diff --git a/internal/ceres/is_close_test.cc b/internal/ceres/is_close_test.cc
index 12d6236..76e4334 100644
--- a/internal/ceres/is_close_test.cc
+++ b/internal/ceres/is_close_test.cc
@@ -34,8 +34,7 @@
 
 #include "gtest/gtest.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 const double kTolerance = 1e-9;
 
@@ -174,5 +173,4 @@
   EXPECT_NEAR(relative_error, 0.0, kTolerance);
   EXPECT_NEAR(absolute_error, 0.0, kTolerance);
 }
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/iterative_refiner.cc b/internal/ceres/iterative_refiner.cc
index 1815469..b9fa88a 100644
--- a/internal/ceres/iterative_refiner.cc
+++ b/internal/ceres/iterative_refiner.cc
@@ -36,8 +36,7 @@
 #include "ceres/sparse_cholesky.h"
 #include "ceres/sparse_matrix.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 IterativeRefiner::IterativeRefiner(const int max_num_iterations)
     : max_num_iterations_(max_num_iterations) {}
@@ -71,5 +70,4 @@
   }
 };
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/iterative_refiner.h b/internal/ceres/iterative_refiner.h
index 837af17..d500212 100644
--- a/internal/ceres/iterative_refiner.h
+++ b/internal/ceres/iterative_refiner.h
@@ -39,8 +39,7 @@
 #include "ceres/internal/eigen.h"
 #include "ceres/internal/export.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 class SparseCholesky;
 class SparseMatrix;
@@ -91,7 +90,6 @@
   Vector lhs_x_solution_;
 };
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_INTERNAL_ITERATIVE_REFINER_H_
diff --git a/internal/ceres/iterative_refiner_test.cc b/internal/ceres/iterative_refiner_test.cc
index e2167b0..3298a44 100644
--- a/internal/ceres/iterative_refiner_test.cc
+++ b/internal/ceres/iterative_refiner_test.cc
@@ -39,8 +39,7 @@
 #include "glog/logging.h"
 #include "gtest/gtest.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 // Macros to help us define virtual methods which we do not expect to
 // use/call in this test.
@@ -163,5 +162,4 @@
               std::numeric_limits<double>::epsilon() * 10);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/iterative_schur_complement_solver.cc b/internal/ceres/iterative_schur_complement_solver.cc
index bc22d68..cc4abd2 100644
--- a/internal/ceres/iterative_schur_complement_solver.cc
+++ b/internal/ceres/iterative_schur_complement_solver.cc
@@ -51,8 +51,7 @@
 #include "ceres/wall_time.h"
 #include "glog/logging.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 IterativeSchurComplementSolver::IterativeSchurComplementSolver(
     LinearSolver::Options options)
@@ -172,5 +171,4 @@
   }
 };
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/iterative_schur_complement_solver.h b/internal/ceres/iterative_schur_complement_solver.h
index 50f4694..c39a94e 100644
--- a/internal/ceres/iterative_schur_complement_solver.h
+++ b/internal/ceres/iterative_schur_complement_solver.h
@@ -39,8 +39,7 @@
 #include "ceres/linear_solver.h"
 #include "ceres/types.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 class BlockSparseMatrix;
 class ImplicitSchurComplement;
@@ -94,8 +93,7 @@
   Vector reduced_linear_system_solution_;
 };
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #include "ceres/internal/reenable_warnings.h"
 
diff --git a/internal/ceres/jet_test.cc b/internal/ceres/jet_test.cc
index 7a8be2a..fe9dbf3 100644
--- a/internal/ceres/jet_test.cc
+++ b/internal/ceres/jet_test.cc
@@ -53,8 +53,7 @@
 #define CERES_NO_FENV_ACCESS
 #endif
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 namespace {
 
@@ -1289,8 +1288,7 @@
 
 #endif  // GTEST_HAS_TYPED_TEST
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #ifdef _MSC_VER
 #pragma float_control(pop)
diff --git a/internal/ceres/jet_traits_test.cc b/internal/ceres/jet_traits_test.cc
index 43afc3c..4d8479b 100644
--- a/internal/ceres/jet_traits_test.cc
+++ b/internal/ceres/jet_traits_test.cc
@@ -34,8 +34,7 @@
 #include <type_traits>
 #include <utility>
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 using J = Jet<double, 2>;
 // Don't care about the dual part for scalar part categorization and comparison
@@ -104,5 +103,4 @@
 static_assert(!PromotableJetOperands_v<Eigen::Matrix<double, 3, 2>, float, int>,
               "Eigen::Matrix must not be Jet promotable");
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/levenberg_marquardt_strategy.cc b/internal/ceres/levenberg_marquardt_strategy.cc
index 2445f5b..88e5ea0 100644
--- a/internal/ceres/levenberg_marquardt_strategy.cc
+++ b/internal/ceres/levenberg_marquardt_strategy.cc
@@ -43,8 +43,7 @@
 #include "ceres/types.h"
 #include "glog/logging.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 LevenbergMarquardtStrategy::LevenbergMarquardtStrategy(
     const TrustRegionStrategy::Options& options)
@@ -161,5 +160,4 @@
 
 double LevenbergMarquardtStrategy::Radius() const { return radius_; }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/levenberg_marquardt_strategy.h b/internal/ceres/levenberg_marquardt_strategy.h
index 4383a49..2b014a6 100644
--- a/internal/ceres/levenberg_marquardt_strategy.h
+++ b/internal/ceres/levenberg_marquardt_strategy.h
@@ -36,8 +36,7 @@
 #include "ceres/internal/export.h"
 #include "ceres/trust_region_strategy.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 // Levenberg-Marquardt step computation and trust region sizing
 // strategy based on on "Methods for Nonlinear Least Squares" by
@@ -84,8 +83,7 @@
   Vector lm_diagonal_;  // lm_diagonal_ = sqrt(diagonal_ / radius_);
 };
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #include "ceres/internal/reenable_warnings.h"
 
diff --git a/internal/ceres/line_search.cc b/internal/ceres/line_search.cc
index 7e7d97f..7bd9c85 100644
--- a/internal/ceres/line_search.cc
+++ b/internal/ceres/line_search.cc
@@ -45,8 +45,7 @@
 #include "ceres/wall_time.h"
 #include "glog/logging.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 using std::map;
 using std::ostream;
@@ -883,5 +882,4 @@
   return true;
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/line_search.h b/internal/ceres/line_search.h
index c2c744a..3632ca5 100644
--- a/internal/ceres/line_search.h
+++ b/internal/ceres/line_search.h
@@ -42,8 +42,7 @@
 #include "ceres/internal/export.h"
 #include "ceres/types.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 class Evaluator;
 class LineSearchFunction;
@@ -302,7 +301,6 @@
                 Summary* summary) const final;
 };
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_INTERNAL_LINE_SEARCH_H_
diff --git a/internal/ceres/line_search_direction.cc b/internal/ceres/line_search_direction.cc
index 98e335a..ae77065 100644
--- a/internal/ceres/line_search_direction.cc
+++ b/internal/ceres/line_search_direction.cc
@@ -38,8 +38,7 @@
 #include "ceres/low_rank_inverse_hessian.h"
 #include "glog/logging.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 class CERES_NO_EXPORT SteepestDescent final : public LineSearchDirection {
  public:
@@ -367,5 +366,4 @@
   return nullptr;
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/line_search_direction.h b/internal/ceres/line_search_direction.h
index 47b256d..c69711b 100644
--- a/internal/ceres/line_search_direction.h
+++ b/internal/ceres/line_search_direction.h
@@ -38,8 +38,7 @@
 #include "ceres/line_search_minimizer.h"
 #include "ceres/types.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 class CERES_NO_EXPORT LineSearchDirection {
  public:
@@ -61,7 +60,6 @@
                              Vector* search_direction) = 0;
 };
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_INTERNAL_LINE_SEARCH_DIRECTION_H_
diff --git a/internal/ceres/line_search_minimizer.cc b/internal/ceres/line_search_minimizer.cc
index ad1e185..b3b2d19 100644
--- a/internal/ceres/line_search_minimizer.cc
+++ b/internal/ceres/line_search_minimizer.cc
@@ -59,8 +59,7 @@
 #include "ceres/wall_time.h"
 #include "glog/logging.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 namespace {
 
 bool EvaluateGradientNorms(Evaluator* evaluator,
@@ -473,5 +472,4 @@
   }
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/line_search_minimizer.h b/internal/ceres/line_search_minimizer.h
index 9a0e994..68936a3 100644
--- a/internal/ceres/line_search_minimizer.h
+++ b/internal/ceres/line_search_minimizer.h
@@ -38,8 +38,7 @@
 #include "ceres/types.h"
 #include "glog/logging.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 // Generic line search minimization algorithm.
 //
@@ -69,7 +68,6 @@
                 Solver::Summary* summary) final;
 };
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_INTERNAL_LINE_SEARCH_MINIMIZER_H_
diff --git a/internal/ceres/line_search_minimizer_test.cc b/internal/ceres/line_search_minimizer_test.cc
index 76a4a47..1c00162 100644
--- a/internal/ceres/line_search_minimizer_test.cc
+++ b/internal/ceres/line_search_minimizer_test.cc
@@ -35,8 +35,7 @@
 #include "glog/logging.h"
 #include "gtest/gtest.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 class QuadraticFirstOrderFunction : public ceres::FirstOrderFunction {
  public:
@@ -62,5 +61,4 @@
   EXPECT_NEAR(summary.final_cost, 0.0, std::numeric_limits<double>::epsilon());
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/line_search_preprocessor.cc b/internal/ceres/line_search_preprocessor.cc
index 26b8d99..4edd68b 100644
--- a/internal/ceres/line_search_preprocessor.cc
+++ b/internal/ceres/line_search_preprocessor.cc
@@ -41,8 +41,7 @@
 #include "ceres/program.h"
 #include "ceres/wall_time.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 namespace {
 
 bool IsProgramValid(const Program& program, std::string* error) {
@@ -102,5 +101,4 @@
   return true;
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/line_search_preprocessor.h b/internal/ceres/line_search_preprocessor.h
index 27e9c2d..8a45aae 100644
--- a/internal/ceres/line_search_preprocessor.h
+++ b/internal/ceres/line_search_preprocessor.h
@@ -35,8 +35,7 @@
 #include "ceres/internal/export.h"
 #include "ceres/preprocessor.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 class CERES_NO_EXPORT LineSearchPreprocessor final : public Preprocessor {
  public:
@@ -45,8 +44,7 @@
                   PreprocessedProblem* preprocessed_problem) final;
 };
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #include "ceres/internal/reenable_warnings.h"
 
diff --git a/internal/ceres/line_search_preprocessor_test.cc b/internal/ceres/line_search_preprocessor_test.cc
index 90cca10..65e3039 100644
--- a/internal/ceres/line_search_preprocessor_test.cc
+++ b/internal/ceres/line_search_preprocessor_test.cc
@@ -37,8 +37,7 @@
 #include "ceres/solver.h"
 #include "gtest/gtest.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST(LineSearchPreprocessor, ZeroProblem) {
   ProblemImpl problem;
@@ -134,5 +133,4 @@
   EXPECT_TRUE(pp.evaluator.get() != nullptr);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/linear_least_squares_problems.cc b/internal/ceres/linear_least_squares_problems.cc
index 2d415af..ab75e6e 100644
--- a/internal/ceres/linear_least_squares_problems.cc
+++ b/internal/ceres/linear_least_squares_problems.cc
@@ -44,8 +44,7 @@
 #include "ceres/types.h"
 #include "glog/logging.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 using std::string;
 
@@ -730,5 +729,4 @@
   return true;
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/linear_least_squares_problems.h b/internal/ceres/linear_least_squares_problems.h
index a1f67eb..7968c46 100644
--- a/internal/ceres/linear_least_squares_problems.h
+++ b/internal/ceres/linear_least_squares_problems.h
@@ -39,8 +39,7 @@
 #include "ceres/internal/export.h"
 #include "ceres/sparse_matrix.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 // Structure defining a linear least squares problem and if possible
 // ground truth solutions. To be used by various LinearSolver tests.
@@ -85,8 +84,7 @@
                                    const double* b,
                                    const double* x,
                                    int num_eliminate_blocks);
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #include "ceres/internal/reenable_warnings.h"
 
diff --git a/internal/ceres/linear_operator.cc b/internal/ceres/linear_operator.cc
index 88b7cc7..597a37e 100644
--- a/internal/ceres/linear_operator.cc
+++ b/internal/ceres/linear_operator.cc
@@ -30,10 +30,8 @@
 
 #include "ceres/linear_operator.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 LinearOperator::~LinearOperator() = default;
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/linear_operator.h b/internal/ceres/linear_operator.h
index c9e6188..f8f2208 100644
--- a/internal/ceres/linear_operator.h
+++ b/internal/ceres/linear_operator.h
@@ -36,8 +36,7 @@
 #include "ceres/internal/export.h"
 #include "ceres/types.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 // This is an abstract base class for linear operators. It supports
 // access to size information and left and right multiply operators.
@@ -54,7 +53,6 @@
   virtual int num_cols() const = 0;
 };
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_INTERNAL_LINEAR_OPERATOR_H_
diff --git a/internal/ceres/linear_solver.cc b/internal/ceres/linear_solver.cc
index fe324f8..d9ef150 100644
--- a/internal/ceres/linear_solver.cc
+++ b/internal/ceres/linear_solver.cc
@@ -43,8 +43,7 @@
 #include "ceres/types.h"
 #include "glog/logging.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 LinearSolver::~LinearSolver() = default;
 
@@ -120,5 +119,4 @@
   }
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/linear_solver.h b/internal/ceres/linear_solver.h
index 2f709c2..d8f3646 100644
--- a/internal/ceres/linear_solver.h
+++ b/internal/ceres/linear_solver.h
@@ -52,8 +52,7 @@
 #include "ceres/types.h"
 #include "glog/logging.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 enum LinearSolverTerminationType {
   // Termination criterion was met.
@@ -338,8 +337,7 @@
 typedef TypedLinearSolver<TripletSparseMatrix>       TripletSparseMatrixSolver;        // NOLINT
 // clang-format on
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #include "ceres/internal/reenable_warnings.h"
 
diff --git a/internal/ceres/low_rank_inverse_hessian.cc b/internal/ceres/low_rank_inverse_hessian.cc
index 2fd1ac8..3e2368f 100644
--- a/internal/ceres/low_rank_inverse_hessian.cc
+++ b/internal/ceres/low_rank_inverse_hessian.cc
@@ -35,8 +35,7 @@
 #include "ceres/internal/eigen.h"
 #include "glog/logging.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 using std::list;
 
@@ -179,5 +178,4 @@
   }
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/low_rank_inverse_hessian.h b/internal/ceres/low_rank_inverse_hessian.h
index 3651936..de30f54 100644
--- a/internal/ceres/low_rank_inverse_hessian.h
+++ b/internal/ceres/low_rank_inverse_hessian.h
@@ -40,8 +40,7 @@
 #include "ceres/internal/export.h"
 #include "ceres/linear_operator.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 // LowRankInverseHessian is a positive definite approximation to the
 // Hessian using the limited memory variant of the
@@ -102,7 +101,6 @@
   std::list<int> indices_;
 };
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_INTERNAL_LOW_RANK_INVERSE_HESSIAN_H_
diff --git a/internal/ceres/manifold_adapter.h b/internal/ceres/manifold_adapter.h
index 9a21456..af4c712 100644
--- a/internal/ceres/manifold_adapter.h
+++ b/internal/ceres/manifold_adapter.h
@@ -3,8 +3,7 @@
 #include "ceres/manifold.h"
 #include "glog/logging.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 // Adapter to wrap LocalParameterization and make them look like Manifolds.
 //
@@ -56,5 +55,4 @@
   const LocalParameterization* local_parameterization_;
 };
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/manifold_test.cc b/internal/ceres/manifold_test.cc
index d136929..310fd9a 100644
--- a/internal/ceres/manifold_test.cc
+++ b/internal/ceres/manifold_test.cc
@@ -49,8 +49,7 @@
 #include "gmock/gmock.h"
 #include "gtest/gtest.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 constexpr int kNumTrials = 1000;
 constexpr double kTolerance = 1e-9;
@@ -931,5 +930,4 @@
   }
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/minimizer.cc b/internal/ceres/minimizer.cc
index 449c728..66fe975 100644
--- a/internal/ceres/minimizer.cc
+++ b/internal/ceres/minimizer.cc
@@ -37,8 +37,7 @@
 #include "ceres/types.h"
 #include "glog/logging.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 std::unique_ptr<Minimizer> Minimizer::Create(MinimizerType minimizer_type) {
   if (minimizer_type == TRUST_REGION) {
@@ -89,5 +88,4 @@
   return false;
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/minimizer.h b/internal/ceres/minimizer.h
index c2c1f71..d4ba708 100644
--- a/internal/ceres/minimizer.h
+++ b/internal/ceres/minimizer.h
@@ -40,8 +40,7 @@
 #include "ceres/iteration_callback.h"
 #include "ceres/solver.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 class Evaluator;
 class SparseMatrix;
@@ -193,8 +192,7 @@
                         Solver::Summary* summary) = 0;
 };
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #include "ceres/internal/reenable_warnings.h"
 
diff --git a/internal/ceres/minimizer_test.cc b/internal/ceres/minimizer_test.cc
index 8ddf126..67de317 100644
--- a/internal/ceres/minimizer_test.cc
+++ b/internal/ceres/minimizer_test.cc
@@ -34,8 +34,7 @@
 #include "ceres/solver.h"
 #include "gtest/gtest.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 class FakeIterationCallback : public IterationCallback {
  public:
@@ -94,5 +93,4 @@
             "User callback returned SOLVER_TERMINATE_SUCCESSFULLY.");
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/normal_prior.cc b/internal/ceres/normal_prior.cc
index 17de40f..abefb5b 100644
--- a/internal/ceres/normal_prior.cc
+++ b/internal/ceres/normal_prior.cc
@@ -31,6 +31,7 @@
 #include "ceres/normal_prior.h"
 
 #include <cstddef>
+#include <utility>
 #include <vector>
 
 #include "ceres/internal/eigen.h"
@@ -39,7 +40,7 @@
 
 namespace ceres {
 
-NormalPrior::NormalPrior(const Matrix& A, const Vector& b) : A_(A), b_(b) {
+NormalPrior::NormalPrior(const Matrix& A, Vector b) : A_(A), b_(std::move(b)) {
   CHECK_GT(b_.rows(), 0);
   CHECK_GT(A_.rows(), 0);
   CHECK_EQ(b_.rows(), A.cols());
diff --git a/internal/ceres/numeric_diff_first_order_function_test.cc b/internal/ceres/numeric_diff_first_order_function_test.cc
index 1926caf..25c58f3 100644
--- a/internal/ceres/numeric_diff_first_order_function_test.cc
+++ b/internal/ceres/numeric_diff_first_order_function_test.cc
@@ -36,8 +36,7 @@
 #include "ceres/first_order_function.h"
 #include "gtest/gtest.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 class QuadraticCostFunctor {
  public:
@@ -75,5 +74,4 @@
   EXPECT_NEAR(gradient[3], parameters[2], kTolerance);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/numeric_diff_test_utils.cc b/internal/ceres/numeric_diff_test_utils.cc
index 95fde0b..3d78e36 100644
--- a/internal/ceres/numeric_diff_test_utils.cc
+++ b/internal/ceres/numeric_diff_test_utils.cc
@@ -39,8 +39,7 @@
 #include "ceres/types.h"
 #include "gtest/gtest.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 bool EasyFunctor::operator()(const double* x1,
                              const double* x2,
@@ -265,5 +264,4 @@
   }
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/numeric_diff_test_utils.h b/internal/ceres/numeric_diff_test_utils.h
index 307c004..68ae5ed 100644
--- a/internal/ceres/numeric_diff_test_utils.h
+++ b/internal/ceres/numeric_diff_test_utils.h
@@ -36,8 +36,7 @@
 #include "ceres/sized_cost_function.h"
 #include "ceres/types.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 // Noise factor for randomized cost function.
 static constexpr double kNoiseFactor = 0.01;
@@ -144,7 +143,6 @@
   RandomizedFunctor functor_;
 };
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_INTERNAL_NUMERIC_DIFF_TEST_UTILS_H_
diff --git a/internal/ceres/ordered_groups_test.cc b/internal/ceres/ordered_groups_test.cc
index d613a41..8b5321b 100644
--- a/internal/ceres/ordered_groups_test.cc
+++ b/internal/ceres/ordered_groups_test.cc
@@ -35,8 +35,7 @@
 
 #include "gtest/gtest.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST(OrderedGroups, EmptyOrderedGroupBehavesCorrectly) {
   ParameterBlockOrdering ordering;
@@ -229,5 +228,4 @@
   // No non-zero groups left.
   EXPECT_DEATH_IF_SUPPORTED(ordering.MinNonZeroGroup(), "NumGroups");
 }
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/pair_hash.h b/internal/ceres/pair_hash.h
index 83ff2b4..acf10eb 100644
--- a/internal/ceres/pair_hash.h
+++ b/internal/ceres/pair_hash.h
@@ -40,8 +40,7 @@
 
 #include "ceres/internal/export.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 #if defined(_WIN32) && !defined(__MINGW64__) && !defined(__MINGW32__)
 #define GG_LONGLONG(x) x##I64
@@ -112,7 +111,6 @@
   }
 };
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_INTERNAL_PAIR_HASH_H_
diff --git a/internal/ceres/parallel_for.h b/internal/ceres/parallel_for.h
index 9528c26..e5599cc 100644
--- a/internal/ceres/parallel_for.h
+++ b/internal/ceres/parallel_for.h
@@ -37,8 +37,7 @@
 #include "ceres/internal/disable_warnings.h"
 #include "ceres/internal/export.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 // Returns the maximum number of threads supported by the threading backend
 // Ceres was compiled with.
@@ -65,8 +64,7 @@
     int end,
     int num_threads,
     const std::function<void(int thread_id, int i)>& function);
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #include "ceres/internal/disable_warnings.h"
 
diff --git a/internal/ceres/parallel_for_cxx.cc b/internal/ceres/parallel_for_cxx.cc
index 5b78db1..f4fd415 100644
--- a/internal/ceres/parallel_for_cxx.cc
+++ b/internal/ceres/parallel_for_cxx.cc
@@ -44,8 +44,7 @@
 #include "ceres/thread_token_provider.h"
 #include "glog/logging.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 namespace {
 // This class creates a thread safe barrier which will block until a
 // pre-specified number of threads call Finished.  This allows us to block the
@@ -239,7 +238,6 @@
   shared_state->block_until_finished.Block();
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_USE_CXX_THREADS
diff --git a/internal/ceres/parallel_for_test.cc b/internal/ceres/parallel_for_test.cc
index b6eb5dc..451d80e 100644
--- a/internal/ceres/parallel_for_test.cc
+++ b/internal/ceres/parallel_for_test.cc
@@ -46,8 +46,7 @@
 #include "gmock/gmock.h"
 #include "gtest/gtest.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 using testing::ElementsAreArray;
 using testing::UnorderedElementsAreArray;
@@ -167,5 +166,4 @@
 }
 #endif  // CERES_NO_THREADS
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/parallel_utils.cc b/internal/ceres/parallel_utils.cc
index e1cb5f9..8e6bcad 100644
--- a/internal/ceres/parallel_utils.cc
+++ b/internal/ceres/parallel_utils.cc
@@ -30,8 +30,7 @@
 
 #include "ceres/parallel_utils.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 void LinearIndexToUpperTriangularIndex(int k, int n, int* i, int* j) {
   // This works by unfolding a rectangle into a triangle.
@@ -86,5 +85,4 @@
   }
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/parallel_utils.h b/internal/ceres/parallel_utils.h
index b2d9e0d..c649757 100644
--- a/internal/ceres/parallel_utils.h
+++ b/internal/ceres/parallel_utils.h
@@ -33,8 +33,7 @@
 
 #include "ceres/internal/export.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 // Converts a linear iteration order into a triangular iteration order.
 // Suppose you have nested loops that look like
@@ -66,7 +65,6 @@
                                                        int* i,
                                                        int* j);
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_INTERNAL_PARALLEL_UTILS_H_
diff --git a/internal/ceres/parallel_utils_test.cc b/internal/ceres/parallel_utils_test.cc
index 4d5a3f6..fd2d792 100644
--- a/internal/ceres/parallel_utils_test.cc
+++ b/internal/ceres/parallel_utils_test.cc
@@ -38,8 +38,7 @@
 #include "glog/logging.h"
 #include "gtest/gtest.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 // Tests that unfolding linear iterations to triangular iterations produces
 // indices that are in-range and unique.
@@ -60,5 +59,4 @@
   }
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/parameter_block.h b/internal/ceres/parameter_block.h
index a9845a3..112d5f8 100644
--- a/internal/ceres/parameter_block.h
+++ b/internal/ceres/parameter_block.h
@@ -47,8 +47,7 @@
 #include "ceres/stringprintf.h"
 #include "glog/logging.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 class ProblemImpl;
 class ResidualBlock;
@@ -382,8 +381,7 @@
   friend class ProblemImpl;
 };
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #include "ceres/internal/reenable_warnings.h"
 
diff --git a/internal/ceres/parameter_block_ordering.cc b/internal/ceres/parameter_block_ordering.cc
index 570a09c..c01eb20 100644
--- a/internal/ceres/parameter_block_ordering.cc
+++ b/internal/ceres/parameter_block_ordering.cc
@@ -42,8 +42,7 @@
 #include "ceres/wall_time.h"
 #include "glog/logging.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 using std::map;
 using std::set;
@@ -171,5 +170,4 @@
   }
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/parameter_block_ordering.h b/internal/ceres/parameter_block_ordering.h
index f9a447a..166fadc 100644
--- a/internal/ceres/parameter_block_ordering.h
+++ b/internal/ceres/parameter_block_ordering.h
@@ -40,8 +40,7 @@
 #include "ceres/ordered_groups.h"
 #include "ceres/types.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 class Program;
 class ParameterBlock;
@@ -88,8 +87,7 @@
 CERES_NO_EXPORT void OrderingToGroupSizes(
     const ParameterBlockOrdering* ordering, std::vector<int>* group_sizes);
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #include "ceres/internal/reenable_warnings.h"
 
diff --git a/internal/ceres/parameter_block_ordering_test.cc b/internal/ceres/parameter_block_ordering_test.cc
index 00ae5f1..68b8772 100644
--- a/internal/ceres/parameter_block_ordering_test.cc
+++ b/internal/ceres/parameter_block_ordering_test.cc
@@ -43,8 +43,7 @@
 #include "ceres/stl_util.h"
 #include "gtest/gtest.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 using VertexSet = std::unordered_set<ParameterBlock*>;
 
@@ -175,5 +174,4 @@
   EXPECT_EQ(ordering.back(), parameter_blocks[0]);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/partitioned_matrix_view.cc b/internal/ceres/partitioned_matrix_view.cc
index d38f30a..2710366 100644
--- a/internal/ceres/partitioned_matrix_view.cc
+++ b/internal/ceres/partitioned_matrix_view.cc
@@ -44,8 +44,7 @@
 #include "ceres/linear_solver.h"
 #include "ceres/partitioned_matrix_view.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 PartitionedMatrixViewBase::~PartitionedMatrixViewBase() = default;
 
@@ -183,5 +182,4 @@
       matrix, options.elimination_groups[0]);
 };
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/partitioned_matrix_view.h b/internal/ceres/partitioned_matrix_view.h
index 5623d3b..36a3450 100644
--- a/internal/ceres/partitioned_matrix_view.h
+++ b/internal/ceres/partitioned_matrix_view.h
@@ -50,8 +50,7 @@
 #include "ceres/small_blas.h"
 #include "glog/logging.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 // Given generalized bi-partite matrix A = [E F], with the same block
 // structure as required by the Schur complement based solver, found
@@ -154,8 +153,7 @@
   int num_cols_f_;
 };
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #include "ceres/internal/reenable_warnings.h"
 
diff --git a/internal/ceres/partitioned_matrix_view_impl.h b/internal/ceres/partitioned_matrix_view_impl.h
index 2e818ca..967620b 100644
--- a/internal/ceres/partitioned_matrix_view_impl.h
+++ b/internal/ceres/partitioned_matrix_view_impl.h
@@ -40,8 +40,7 @@
 #include "ceres/small_blas.h"
 #include "glog/logging.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 template <int kRowBlockSize, int kEBlockSize, int kFBlockSize>
 PartitionedMatrixView<kRowBlockSize, kEBlockSize, kFBlockSize>::
@@ -380,5 +379,4 @@
   }
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/partitioned_matrix_view_template.py b/internal/ceres/partitioned_matrix_view_template.py
index a197083..27f368f 100644
--- a/internal/ceres/partitioned_matrix_view_template.py
+++ b/internal/ceres/partitioned_matrix_view_template.py
@@ -91,15 +91,13 @@
 DYNAMIC_FILE = """
 #include "ceres/partitioned_matrix_view_impl.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 template class PartitionedMatrixView<%s,
                                      %s,
                                      %s>;
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 """
 
 SPECIALIZATION_FILE = """
@@ -110,13 +108,11 @@
 
 #include "ceres/partitioned_matrix_view_impl.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 template class PartitionedMatrixView<%s, %s, %s>;
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_RESTRICT_SCHUR_SPECIALIZATION
 """
@@ -127,8 +123,7 @@
 #include "ceres/linear_solver.h"
 #include "ceres/partitioned_matrix_view.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 PartitionedMatrixViewBase::~PartitionedMatrixViewBase() = default;
 
@@ -150,6 +145,5 @@
       matrix, options.elimination_groups[0]);
 };
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 """
diff --git a/internal/ceres/polynomial.cc b/internal/ceres/polynomial.cc
index 96267aa..a3e790d 100644
--- a/internal/ceres/polynomial.cc
+++ b/internal/ceres/polynomial.cc
@@ -40,8 +40,7 @@
 #include "ceres/internal/export.h"
 #include "glog/logging.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 using std::vector;
 
@@ -389,5 +388,4 @@
   }
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/polynomial.h b/internal/ceres/polynomial.h
index 3ca753c..02db68a 100644
--- a/internal/ceres/polynomial.h
+++ b/internal/ceres/polynomial.h
@@ -38,8 +38,7 @@
 #include "ceres/internal/eigen.h"
 #include "ceres/internal/export.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 struct FunctionSample;
 
@@ -116,8 +115,7 @@
     double* optimal_x,
     double* optimal_value);
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #include "ceres/internal/reenable_warnings.h"
 
diff --git a/internal/ceres/polynomial_test.cc b/internal/ceres/polynomial_test.cc
index c45557e..6b6d718 100644
--- a/internal/ceres/polynomial_test.cc
+++ b/internal/ceres/polynomial_test.cc
@@ -40,8 +40,7 @@
 #include "ceres/test_util.h"
 #include "gtest/gtest.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 using std::vector;
 
@@ -512,5 +511,4 @@
   EXPECT_NEAR((true_polynomial - polynomial).norm(), 0.0, 1e-14);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/preconditioner.cc b/internal/ceres/preconditioner.cc
index 17b9629c..391e1b5 100644
--- a/internal/ceres/preconditioner.cc
+++ b/internal/ceres/preconditioner.cc
@@ -32,8 +32,7 @@
 
 #include "glog/logging.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 Preconditioner::~Preconditioner() = default;
 
@@ -70,5 +69,4 @@
   return matrix_->num_rows();
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/preconditioner.h b/internal/ceres/preconditioner.h
index 6433cc7..fdc4d86 100644
--- a/internal/ceres/preconditioner.h
+++ b/internal/ceres/preconditioner.h
@@ -42,8 +42,7 @@
 #include "ceres/sparse_matrix.h"
 #include "ceres/types.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 class BlockSparseMatrix;
 class SparseMatrix;
@@ -183,8 +182,7 @@
   const SparseMatrix* matrix_;
 };
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #include "ceres/internal/reenable_warnings.h"
 
diff --git a/internal/ceres/preprocessor.cc b/internal/ceres/preprocessor.cc
index 44f0974..9d60ef9 100644
--- a/internal/ceres/preprocessor.cc
+++ b/internal/ceres/preprocessor.cc
@@ -40,8 +40,7 @@
 #include "ceres/solver.h"
 #include "ceres/trust_region_preprocessor.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 std::unique_ptr<Preprocessor> Preprocessor::Create(
     MinimizerType minimizer_type) {
@@ -104,5 +103,4 @@
   }
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/preprocessor.h b/internal/ceres/preprocessor.h
index b5db80a..282a8f0 100644
--- a/internal/ceres/preprocessor.h
+++ b/internal/ceres/preprocessor.h
@@ -47,8 +47,7 @@
 #include "ceres/program.h"
 #include "ceres/solver.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 struct PreprocessedProblem;
 
@@ -118,8 +117,7 @@
 CERES_NO_EXPORT
 void SetupCommonMinimizerOptions(PreprocessedProblem* pp);
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #include "ceres/internal/reenable_warnings.h"
 
diff --git a/internal/ceres/problem_impl.cc b/internal/ceres/problem_impl.cc
index 01a22c1..8549097 100644
--- a/internal/ceres/problem_impl.cc
+++ b/internal/ceres/problem_impl.cc
@@ -64,8 +64,7 @@
 #include "ceres/stringprintf.h"
 #include "glog/logging.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 namespace {
 // Returns true if two regions of memory, a and b, with sizes size_a and size_b
 // respectively, overlap.
@@ -968,5 +967,4 @@
   }
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/problem_test.cc b/internal/ceres/problem_test.cc
index f424c7e..d7ec1f9 100644
--- a/internal/ceres/problem_test.cc
+++ b/internal/ceres/problem_test.cc
@@ -51,8 +51,7 @@
 #include "gmock/gmock.h"
 #include "gtest/gtest.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 using std::vector;
 
@@ -2805,5 +2804,4 @@
                                             jacobians));
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/program.cc b/internal/ceres/program.cc
index 1cb9ebc..9a4ecf3 100644
--- a/internal/ceres/program.cc
+++ b/internal/ceres/program.cc
@@ -51,8 +51,7 @@
 #include "ceres/stl_util.h"
 #include "ceres/triplet_sparse_matrix.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 const std::vector<ParameterBlock*>& Program::parameter_blocks() const {
   return parameter_blocks_;
@@ -545,5 +544,4 @@
   return ret;
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/program.h b/internal/ceres/program.h
index 4dbd1ba..cb923ae 100644
--- a/internal/ceres/program.h
+++ b/internal/ceres/program.h
@@ -40,8 +40,7 @@
 #include "ceres/internal/disable_warnings.h"
 #include "ceres/internal/export.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 class ParameterBlock;
 class ProblemImpl;
@@ -192,8 +191,7 @@
   friend class ProblemImpl;
 };
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #include "ceres/internal/reenable_warnings.h"
 
diff --git a/internal/ceres/reorder_program.cc b/internal/ceres/reorder_program.cc
index d552ebf..4e75c3f 100644
--- a/internal/ceres/reorder_program.cc
+++ b/internal/ceres/reorder_program.cc
@@ -56,8 +56,7 @@
 
 #include "glog/logging.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 using std::map;
 using std::set;
@@ -575,5 +574,4 @@
   return it - residual_blocks->begin();
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/reorder_program.h b/internal/ceres/reorder_program.h
index fbc4923..64f4095 100644
--- a/internal/ceres/reorder_program.h
+++ b/internal/ceres/reorder_program.h
@@ -39,8 +39,7 @@
 #include "ceres/problem_impl.h"
 #include "ceres/types.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 class Program;
 
@@ -112,8 +111,7 @@
     const std::unordered_set<ResidualBlockId>& bottom_residual_blocks,
     Program* program);
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #include "ceres/internal/reenable_warnings.h"
 
diff --git a/internal/ceres/residual_block.cc b/internal/ceres/residual_block.cc
index cd408f2..93c045f 100644
--- a/internal/ceres/residual_block.cc
+++ b/internal/ceres/residual_block.cc
@@ -47,8 +47,7 @@
 
 using Eigen::Dynamic;
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 ResidualBlock::ResidualBlock(
     const CostFunction* cost_function,
@@ -216,5 +215,4 @@
   return scratch_doubles;
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/residual_block_test.cc b/internal/ceres/residual_block_test.cc
index f01d842..2864ee1 100644
--- a/internal/ceres/residual_block_test.cc
+++ b/internal/ceres/residual_block_test.cc
@@ -38,8 +38,7 @@
 #include "ceres/sized_cost_function.h"
 #include "gtest/gtest.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 using std::vector;
 
@@ -324,5 +323,4 @@
   EXPECT_EQ(expected_jacobian_rz, jacobian_rz);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/residual_block_utils.cc b/internal/ceres/residual_block_utils.cc
index 11c7623..7dc5d44 100644
--- a/internal/ceres/residual_block_utils.cc
+++ b/internal/ceres/residual_block_utils.cc
@@ -42,8 +42,7 @@
 #include "ceres/stringprintf.h"
 #include "glog/logging.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 using std::string;
 
@@ -141,5 +140,4 @@
   return true;
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/residual_block_utils.h b/internal/ceres/residual_block_utils.h
index f75b6ae..38c75bf 100644
--- a/internal/ceres/residual_block_utils.h
+++ b/internal/ceres/residual_block_utils.h
@@ -47,8 +47,7 @@
 
 #include "ceres/internal/export.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 class ResidualBlock;
 
@@ -78,7 +77,6 @@
                                double* residuals,
                                double** jacobians);
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_INTERNAL_RESIDUAL_BLOCK_UTILS_H_
diff --git a/internal/ceres/schur_complement_solver.cc b/internal/ceres/schur_complement_solver.cc
index bb442b4..693b519 100644
--- a/internal/ceres/schur_complement_solver.cc
+++ b/internal/ceres/schur_complement_solver.cc
@@ -52,8 +52,7 @@
 #include "ceres/types.h"
 #include "ceres/wall_time.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 using std::make_pair;
 using std::pair;
@@ -414,5 +413,4 @@
       lhs_adapter.get(), rhs(), cg_per_solve_options, solution);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/schur_complement_solver.h b/internal/ceres/schur_complement_solver.h
index 859a086..0d069eb 100644
--- a/internal/ceres/schur_complement_solver.h
+++ b/internal/ceres/schur_complement_solver.h
@@ -54,8 +54,7 @@
 
 #include "ceres/internal/disable_warnings.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 class BlockSparseMatrix;
 class SparseCholesky;
@@ -191,8 +190,7 @@
   std::unique_ptr<BlockRandomAccessDiagonalMatrix> preconditioner_;
 };
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #include "ceres/internal/reenable_warnings.h"
 
diff --git a/internal/ceres/schur_complement_solver_test.cc b/internal/ceres/schur_complement_solver_test.cc
index e943ed1..2df8267 100644
--- a/internal/ceres/schur_complement_solver_test.cc
+++ b/internal/ceres/schur_complement_solver_test.cc
@@ -45,8 +45,7 @@
 #include "glog/logging.h"
 #include "gtest/gtest.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 class SchurComplementSolverTest : public ::testing::Test {
  protected:
@@ -244,5 +243,4 @@
 }
 #endif  // CERES_USE_EIGEN_SPARSE
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/schur_eliminator.cc b/internal/ceres/schur_eliminator.cc
index 22e7358..4515c42 100644
--- a/internal/ceres/schur_eliminator.cc
+++ b/internal/ceres/schur_eliminator.cc
@@ -44,8 +44,7 @@
 #include "ceres/linear_solver.h"
 #include "ceres/schur_eliminator.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 SchurEliminatorBase::~SchurEliminatorBase() = default;
 
@@ -161,5 +160,4 @@
                                           Eigen::Dynamic>>(options);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/schur_eliminator.h b/internal/ceres/schur_eliminator.h
index 91831dc..75be5ae 100644
--- a/internal/ceres/schur_eliminator.h
+++ b/internal/ceres/schur_eliminator.h
@@ -46,8 +46,7 @@
 #include "ceres/internal/export.h"
 #include "ceres/linear_solver.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 // Classes implementing the SchurEliminatorBase interface implement
 // variable elimination for linear least squares problems. Assuming
@@ -623,8 +622,7 @@
   std::vector<double> e_t_e_inverse_matrices_;
 };
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #include "ceres/internal/reenable_warnings.h"
 
diff --git a/internal/ceres/schur_eliminator_benchmark.cc b/internal/ceres/schur_eliminator_benchmark.cc
index 4e19582..2bb18ca 100644
--- a/internal/ceres/schur_eliminator_benchmark.cc
+++ b/internal/ceres/schur_eliminator_benchmark.cc
@@ -38,8 +38,7 @@
 #include "ceres/random.h"
 #include "ceres/schur_eliminator.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 constexpr int kRowBlockSize = 2;
 constexpr int kEBlockSize = 3;
@@ -219,7 +218,6 @@
 BENCHMARK(BM_SchurEliminatorBackSubstitute)->Range(10, 10000);
 BENCHMARK(BM_SchurEliminatorForOneFBlockBackSubstitute)->Range(10, 10000);
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 BENCHMARK_MAIN();
diff --git a/internal/ceres/schur_eliminator_impl.h b/internal/ceres/schur_eliminator_impl.h
index de3ba3e..9ad0ebd 100644
--- a/internal/ceres/schur_eliminator_impl.h
+++ b/internal/ceres/schur_eliminator_impl.h
@@ -69,8 +69,7 @@
 #include "ceres/thread_token_provider.h"
 #include "glog/logging.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 template <int kRowBlockSize, int kEBlockSize, int kFBlockSize>
 SchurEliminator<kRowBlockSize, kEBlockSize, kFBlockSize>::~SchurEliminator() {
@@ -716,7 +715,6 @@
   }
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_INTERNAL_SCHUR_ELIMINATOR_IMPL_H_
diff --git a/internal/ceres/schur_eliminator_template.py b/internal/ceres/schur_eliminator_template.py
index 62a5f2f..d0d4adb 100644
--- a/internal/ceres/schur_eliminator_template.py
+++ b/internal/ceres/schur_eliminator_template.py
@@ -95,13 +95,11 @@
 DYNAMIC_FILE = """
 #include "ceres/schur_eliminator_impl.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 template class SchurEliminator<%s, %s, %s>;
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 """
 
 SPECIALIZATION_FILE = """
@@ -112,13 +110,11 @@
 
 #include "ceres/schur_eliminator_impl.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 template class SchurEliminator<%s, %s, %s>;
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_RESTRICT_SCHUR_SPECIALIZATION
 """
@@ -129,8 +125,7 @@
 #include "ceres/linear_solver.h"
 #include "ceres/schur_eliminator.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 SchurEliminatorBase::~SchurEliminatorBase() = default;
 
@@ -151,6 +146,5 @@
                                           Eigen::Dynamic>>(options);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 """
diff --git a/internal/ceres/schur_eliminator_test.cc b/internal/ceres/schur_eliminator_test.cc
index 0b20d70..a8c5f71 100644
--- a/internal/ceres/schur_eliminator_test.cc
+++ b/internal/ceres/schur_eliminator_test.cc
@@ -51,8 +51,7 @@
 // TODO(sameeragarwal): Reduce the size of these tests and redo the
 // parameterization to be more efficient.
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 class SchurEliminatorTest : public ::testing::Test {
  protected:
@@ -369,5 +368,4 @@
       << actual_e_sol;
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/schur_jacobi_preconditioner.cc b/internal/ceres/schur_jacobi_preconditioner.cc
index 3ecec72..d452ba4 100644
--- a/internal/ceres/schur_jacobi_preconditioner.cc
+++ b/internal/ceres/schur_jacobi_preconditioner.cc
@@ -39,8 +39,7 @@
 #include "ceres/schur_eliminator.h"
 #include "glog/logging.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 SchurJacobiPreconditioner::SchurJacobiPreconditioner(
     const CompressedRowBlockStructure& bs, Preconditioner::Options options)
@@ -99,5 +98,4 @@
 
 int SchurJacobiPreconditioner::num_rows() const { return m_->num_rows(); }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/schur_jacobi_preconditioner.h b/internal/ceres/schur_jacobi_preconditioner.h
index a43bc33..76a7b3d 100644
--- a/internal/ceres/schur_jacobi_preconditioner.h
+++ b/internal/ceres/schur_jacobi_preconditioner.h
@@ -47,8 +47,7 @@
 #include "ceres/internal/export.h"
 #include "ceres/preconditioner.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 class BlockRandomAccessDiagonalMatrix;
 class BlockSparseMatrix;
@@ -104,8 +103,7 @@
   std::unique_ptr<BlockRandomAccessDiagonalMatrix> m_;
 };
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #include "ceres/internal/reenable_warnings.h"
 
diff --git a/internal/ceres/schur_templates.h b/internal/ceres/schur_templates.h
index cacee20..fe28113 100644
--- a/internal/ceres/schur_templates.h
+++ b/internal/ceres/schur_templates.h
@@ -36,14 +36,12 @@
 #include "ceres/internal/export.h"
 #include "ceres/linear_solver.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 CERES_NO_EXPORT
 void GetBestSchurTemplateSpecialization(int* row_block_size,
                                         int* e_block_size,
                                         int* f_block_size);
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_INTERNAL_SCHUR_TEMPLATES_H_
diff --git a/internal/ceres/scoped_thread_token.h b/internal/ceres/scoped_thread_token.h
index 533bfd5..5bb083c 100644
--- a/internal/ceres/scoped_thread_token.h
+++ b/internal/ceres/scoped_thread_token.h
@@ -34,8 +34,7 @@
 #include "ceres/internal/export.h"
 #include "ceres/thread_token_provider.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 // Helper class for ThreadTokenProvider. This object acquires a token in its
 // constructor and puts that token back with destruction.
@@ -55,7 +54,6 @@
   int token_;
 };
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_INTERNAL_SCOPED_THREAD_TOKEN_H_
diff --git a/internal/ceres/scratch_evaluate_preparer.cc b/internal/ceres/scratch_evaluate_preparer.cc
index 0a1b0f3..680dab9 100644
--- a/internal/ceres/scratch_evaluate_preparer.cc
+++ b/internal/ceres/scratch_evaluate_preparer.cc
@@ -36,8 +36,7 @@
 #include "ceres/program.h"
 #include "ceres/residual_block.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 std::unique_ptr<ScratchEvaluatePreparer[]> ScratchEvaluatePreparer::Create(
     const Program& program, int num_threads) {
@@ -75,5 +74,4 @@
   }
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/scratch_evaluate_preparer.h b/internal/ceres/scratch_evaluate_preparer.h
index 3f4e7df..946244b 100644
--- a/internal/ceres/scratch_evaluate_preparer.h
+++ b/internal/ceres/scratch_evaluate_preparer.h
@@ -40,8 +40,7 @@
 #include "ceres/internal/disable_warnings.h"
 #include "ceres/internal/export.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 class Program;
 class ResidualBlock;
@@ -66,8 +65,7 @@
   std::unique_ptr<double[]> jacobian_scratch_;
 };
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #include "ceres/internal/reenable_warnings.h"
 
diff --git a/internal/ceres/single_linkage_clustering.cc b/internal/ceres/single_linkage_clustering.cc
index 0e78131..8772c0c 100644
--- a/internal/ceres/single_linkage_clustering.cc
+++ b/internal/ceres/single_linkage_clustering.cc
@@ -36,8 +36,7 @@
 #include "ceres/graph.h"
 #include "ceres/graph_algorithms.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 int ComputeSingleLinkageClustering(
     const SingleLinkageClusteringOptions& options,
@@ -91,5 +90,4 @@
   return num_clusters;
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/single_linkage_clustering.h b/internal/ceres/single_linkage_clustering.h
index b4a7e07..9d334ca 100644
--- a/internal/ceres/single_linkage_clustering.h
+++ b/internal/ceres/single_linkage_clustering.h
@@ -37,8 +37,7 @@
 #include "ceres/internal/disable_warnings.h"
 #include "ceres/internal/export.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 struct SingleLinkageClusteringOptions {
   // Graph edges with edge weight less than min_similarity are ignored
@@ -61,8 +60,7 @@
     const WeightedGraph<int>& graph,
     std::unordered_map<int, int>* membership);
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #include "ceres/internal/reenable_warnings.h"
 
diff --git a/internal/ceres/single_linkage_clustering_test.cc b/internal/ceres/single_linkage_clustering_test.cc
index 28c7c41..17b03b7 100644
--- a/internal/ceres/single_linkage_clustering_test.cc
+++ b/internal/ceres/single_linkage_clustering_test.cc
@@ -35,8 +35,7 @@
 #include "ceres/graph.h"
 #include "gtest/gtest.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST(SingleLinkageClustering, GraphHasTwoComponents) {
   WeightedGraph<int> graph;
@@ -122,5 +121,4 @@
   EXPECT_EQ(membership[4], membership[5]);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/small_blas.h b/internal/ceres/small_blas.h
index 1cf41a5..ec26be3 100644
--- a/internal/ceres/small_blas.h
+++ b/internal/ceres/small_blas.h
@@ -40,8 +40,7 @@
 #include "glog/logging.h"
 #include "small_blas_generic.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 // The following three macros are used to share code and reduce
 // template junk across the various GEMM variants.
@@ -561,7 +560,6 @@
 #undef CERES_GEMM_STORE_SINGLE
 #undef CERES_GEMM_STORE_PAIR
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_INTERNAL_SMALL_BLAS_H_
diff --git a/internal/ceres/small_blas_gemm_benchmark.cc b/internal/ceres/small_blas_gemm_benchmark.cc
index f146ba6..7239cf4 100644
--- a/internal/ceres/small_blas_gemm_benchmark.cc
+++ b/internal/ceres/small_blas_gemm_benchmark.cc
@@ -34,8 +34,7 @@
 #include "benchmark/benchmark.h"
 #include "ceres/small_blas.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 // Benchmarking matrix-matrix multiply routines and optimizing memory
 // access requires that we make sure that they are not just sitting in
@@ -213,7 +212,6 @@
 #undef BENCHMARK_DYNAMIC_MMT_FN
 #undef BENCHMARK_STATIC_MMT_FN
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 BENCHMARK_MAIN();
diff --git a/internal/ceres/small_blas_generic.h b/internal/ceres/small_blas_generic.h
index dd21f59..28571d7 100644
--- a/internal/ceres/small_blas_generic.h
+++ b/internal/ceres/small_blas_generic.h
@@ -35,8 +35,7 @@
 #ifndef CERES_INTERNAL_SMALL_BLAS_GENERIC_H_
 #define CERES_INTERNAL_SMALL_BLAS_GENERIC_H_
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 // The following macros are used to share code
 #define CERES_GEMM_OPT_NAIVE_HEADER       \
@@ -311,7 +310,6 @@
 #undef CERES_GEMM_OPT_NAIVE_HEADER
 #undef CERES_GEMM_OPT_STORE_MAT1X4
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_INTERNAL_SMALL_BLAS_GENERIC_H_
diff --git a/internal/ceres/solver_test.cc b/internal/ceres/solver_test.cc
index 7b34bf2..e73e899 100644
--- a/internal/ceres/solver_test.cc
+++ b/internal/ceres/solver_test.cc
@@ -44,8 +44,7 @@
 #include "ceres/sized_cost_function.h"
 #include "gtest/gtest.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 using std::string;
 
@@ -551,5 +550,4 @@
   EXPECT_EQ(y, 1.0);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/solver_utils.cc b/internal/ceres/solver_utils.cc
index 22fa137..d1bac1a 100644
--- a/internal/ceres/solver_utils.cc
+++ b/internal/ceres/solver_utils.cc
@@ -40,8 +40,7 @@
 #include "cuda_runtime.h"
 #endif  // CERES_NO_CUDA
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 // clang-format off
 #define CERES_EIGEN_VERSION                 \
@@ -97,5 +96,4 @@
   return value;
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/solver_utils.h b/internal/ceres/solver_utils.h
index 298564a..7261055 100644
--- a/internal/ceres/solver_utils.h
+++ b/internal/ceres/solver_utils.h
@@ -39,8 +39,7 @@
 #include "ceres/iteration_callback.h"
 #include "ceres/types.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 template <typename SummaryType>
 bool IsSolutionUsable(const SummaryType& summary) {
@@ -63,8 +62,7 @@
 CERES_NO_EXPORT
 std::string VersionString();
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #include "ceres/internal/reenable_warnings.h"
 
diff --git a/internal/ceres/sparse_cholesky.cc b/internal/ceres/sparse_cholesky.cc
index 4a80470..9080b34 100644
--- a/internal/ceres/sparse_cholesky.cc
+++ b/internal/ceres/sparse_cholesky.cc
@@ -40,8 +40,7 @@
 #include "ceres/iterative_refiner.h"
 #include "ceres/suitesparse.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 std::unique_ptr<SparseCholesky> SparseCholesky::Create(
     const LinearSolver::Options& options) {
@@ -161,5 +160,4 @@
   return LINEAR_SOLVER_SUCCESS;
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/sparse_cholesky.h b/internal/ceres/sparse_cholesky.h
index 80c5cb2..831beee 100644
--- a/internal/ceres/sparse_cholesky.h
+++ b/internal/ceres/sparse_cholesky.h
@@ -43,8 +43,7 @@
 #include "ceres/linear_solver.h"
 #include "glog/logging.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 // An interface that abstracts away the internal details of various
 // sparse linear algebra libraries and offers a simple API for solving
@@ -135,8 +134,7 @@
   CompressedRowSparseMatrix* lhs_ = nullptr;
 };
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #include "ceres/internal/reenable_warnings.h"
 
diff --git a/internal/ceres/sparse_cholesky_test.cc b/internal/ceres/sparse_cholesky_test.cc
index 9e47acf..00480f4 100644
--- a/internal/ceres/sparse_cholesky_test.cc
+++ b/internal/ceres/sparse_cholesky_test.cc
@@ -47,8 +47,7 @@
 #include "gmock/gmock.h"
 #include "gtest/gtest.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 namespace {
 
@@ -348,5 +347,4 @@
 
 }  // namespace
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/sparse_matrix.cc b/internal/ceres/sparse_matrix.cc
index bc757ea..40899bb 100644
--- a/internal/ceres/sparse_matrix.cc
+++ b/internal/ceres/sparse_matrix.cc
@@ -30,10 +30,8 @@
 
 #include "ceres/sparse_matrix.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 SparseMatrix::~SparseMatrix() = default;
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/sparse_matrix.h b/internal/ceres/sparse_matrix.h
index 1dbb96e..9fe33a3 100644
--- a/internal/ceres/sparse_matrix.h
+++ b/internal/ceres/sparse_matrix.h
@@ -40,8 +40,7 @@
 #include "ceres/linear_operator.h"
 #include "ceres/types.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 // This class defines the interface for storing and manipulating
 // sparse matrices. The key property that differentiates different
@@ -103,7 +102,6 @@
   virtual int num_nonzeros() const = 0;
 };
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_INTERNAL_SPARSE_MATRIX_H_
diff --git a/internal/ceres/sparse_normal_cholesky_solver.cc b/internal/ceres/sparse_normal_cholesky_solver.cc
index 2e52ae6..b5030c7 100644
--- a/internal/ceres/sparse_normal_cholesky_solver.cc
+++ b/internal/ceres/sparse_normal_cholesky_solver.cc
@@ -45,8 +45,7 @@
 #include "ceres/types.h"
 #include "ceres/wall_time.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 SparseNormalCholeskySolver::SparseNormalCholeskySolver(
     const LinearSolver::Options& options)
@@ -110,5 +109,4 @@
   return summary;
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/sparse_normal_cholesky_solver.h b/internal/ceres/sparse_normal_cholesky_solver.h
index caec566..31d002c 100644
--- a/internal/ceres/sparse_normal_cholesky_solver.h
+++ b/internal/ceres/sparse_normal_cholesky_solver.h
@@ -45,8 +45,7 @@
 #include "ceres/internal/export.h"
 #include "ceres/linear_solver.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 class CompressedRowSparseMatrix;
 class InnerProductComputer;
@@ -75,7 +74,6 @@
   std::unique_ptr<InnerProductComputer> inner_product_computer_;
 };
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_INTERNAL_SPARSE_NORMAL_CHOLESKY_SOLVER_H_
diff --git a/internal/ceres/sparse_normal_cholesky_solver_test.cc b/internal/ceres/sparse_normal_cholesky_solver_test.cc
index 2b00dcd..eaf2dbb 100644
--- a/internal/ceres/sparse_normal_cholesky_solver_test.cc
+++ b/internal/ceres/sparse_normal_cholesky_solver_test.cc
@@ -41,8 +41,7 @@
 #include "glog/logging.h"
 #include "gtest/gtest.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 // TODO(sameeragarwal): These tests needs to be re-written, since
 // SparseNormalCholeskySolver is a composition of two classes now,
@@ -202,5 +201,4 @@
 }
 #endif  // CERES_USE_EIGEN_SPARSE
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/stringprintf.cc b/internal/ceres/stringprintf.cc
index e45b430..1b6b6ff 100644
--- a/internal/ceres/stringprintf.cc
+++ b/internal/ceres/stringprintf.cc
@@ -38,8 +38,7 @@
 
 #include "ceres/internal/export.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 using std::string;
 
@@ -118,5 +117,4 @@
   va_end(ap);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/stringprintf.h b/internal/ceres/stringprintf.h
index e24325f..3a774a4 100644
--- a/internal/ceres/stringprintf.h
+++ b/internal/ceres/stringprintf.h
@@ -44,8 +44,7 @@
 #include "ceres/internal/disable_warnings.h"
 #include "ceres/internal/export.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 #if (defined(__GNUC__) || defined(__clang__))
 // Tell the compiler to do printf format string checking if the compiler
@@ -90,8 +89,7 @@
 
 #undef CERES_PRINTF_ATTRIBUTE
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #include "ceres/internal/reenable_warnings.h"
 
diff --git a/internal/ceres/subset_preconditioner.cc b/internal/ceres/subset_preconditioner.cc
index 221530c..b9202db 100644
--- a/internal/ceres/subset_preconditioner.cc
+++ b/internal/ceres/subset_preconditioner.cc
@@ -40,8 +40,7 @@
 #include "ceres/sparse_cholesky.h"
 #include "ceres/types.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 SubsetPreconditioner::SubsetPreconditioner(Preconditioner::Options options,
                                            const BlockSparseMatrix& A)
@@ -114,5 +113,4 @@
   return true;
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/subset_preconditioner.h b/internal/ceres/subset_preconditioner.h
index 6d07995..1f1c6ec 100644
--- a/internal/ceres/subset_preconditioner.h
+++ b/internal/ceres/subset_preconditioner.h
@@ -37,8 +37,7 @@
 #include "ceres/internal/export.h"
 #include "ceres/preconditioner.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 class BlockSparseMatrix;
 class SparseCholesky;
@@ -89,8 +88,7 @@
   std::unique_ptr<InnerProductComputer> inner_product_computer_;
 };
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #include "ceres/internal/reenable_warnings.h"
 
diff --git a/internal/ceres/subset_preconditioner_test.cc b/internal/ceres/subset_preconditioner_test.cc
index a6b3e7f..bc517e7 100644
--- a/internal/ceres/subset_preconditioner_test.cc
+++ b/internal/ceres/subset_preconditioner_test.cc
@@ -42,8 +42,7 @@
 #include "glog/logging.h"
 #include "gtest/gtest.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 namespace {
 
@@ -206,5 +205,4 @@
                          ParamInfoToString);
 #endif
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/suitesparse.cc b/internal/ceres/suitesparse.cc
index 883dcc8..bac5327 100644
--- a/internal/ceres/suitesparse.cc
+++ b/internal/ceres/suitesparse.cc
@@ -42,8 +42,7 @@
 #include "ceres/triplet_sparse_matrix.h"
 #include "cholmod.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 using std::string;
 using std::vector;
@@ -425,7 +424,6 @@
   return LINEAR_SOLVER_SUCCESS;
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_NO_SUITESPARSE
diff --git a/internal/ceres/suitesparse.h b/internal/ceres/suitesparse.h
index 3f62e7c..f7bf3b1 100644
--- a/internal/ceres/suitesparse.h
+++ b/internal/ceres/suitesparse.h
@@ -73,8 +73,7 @@
 
 #include "ceres/internal/disable_warnings.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 class CompressedRowSparseMatrix;
 class TripletSparseMatrix;
@@ -312,8 +311,7 @@
   cholmod_factor* factor_;
 };
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #include "ceres/internal/reenable_warnings.h"
 
diff --git a/internal/ceres/system_test.cc b/internal/ceres/system_test.cc
index 9d66eb0..89be241 100644
--- a/internal/ceres/system_test.cc
+++ b/internal/ceres/system_test.cc
@@ -43,8 +43,7 @@
 #include "glog/logging.h"
 #include "gtest/gtest.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 // This class implements the SystemTestProblem interface and provides
 // access to an implementation of Powell's singular function.
@@ -220,5 +219,4 @@
 }
 #endif  // CERES_USE_EIGEN_SPARSE
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/thread_pool.cc b/internal/ceres/thread_pool.cc
index 57f01af..1fd1a4c 100644
--- a/internal/ceres/thread_pool.cc
+++ b/internal/ceres/thread_pool.cc
@@ -38,8 +38,7 @@
 
 #include "ceres/thread_pool.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 namespace {
 
 // Constrain the total number of threads to the amount the hardware can support.
@@ -105,7 +104,6 @@
 
 void ThreadPool::Stop() { task_queue_.StopWaiters(); }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_USE_CXX_THREADS
diff --git a/internal/ceres/thread_pool.h b/internal/ceres/thread_pool.h
index 94ab1e6..ff47f10 100644
--- a/internal/ceres/thread_pool.h
+++ b/internal/ceres/thread_pool.h
@@ -39,8 +39,7 @@
 #include "ceres/concurrent_queue.h"
 #include "ceres/internal/export.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 // A thread-safe thread pool with an unbounded task queue and a resizable number
 // of workers.  The size of the thread pool can be increased but never decreased
@@ -115,7 +114,6 @@
   std::mutex thread_pool_mutex_;
 };
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_INTERNAL_THREAD_POOL_H_
diff --git a/internal/ceres/thread_pool_test.cc b/internal/ceres/thread_pool_test.cc
index b204cf3..e64011d 100644
--- a/internal/ceres/thread_pool_test.cc
+++ b/internal/ceres/thread_pool_test.cc
@@ -43,8 +43,7 @@
 #include "gmock/gmock.h"
 #include "gtest/gtest.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 // Adds a number of tasks to the thread pool and ensures they all run.
 TEST(ThreadPool, AddTask) {
@@ -193,7 +192,6 @@
   EXPECT_EQ(2, thread_pool.Size());
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_USE_CXX_THREADS
diff --git a/internal/ceres/thread_token_provider.cc b/internal/ceres/thread_token_provider.cc
index c7ec67f..e48964c 100644
--- a/internal/ceres/thread_token_provider.cc
+++ b/internal/ceres/thread_token_provider.cc
@@ -34,8 +34,7 @@
 #include <omp.h>
 #endif
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 ThreadTokenProvider::ThreadTokenProvider(int num_threads) {
   (void)num_threads;
@@ -69,5 +68,4 @@
 #endif
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/thread_token_provider.h b/internal/ceres/thread_token_provider.h
index 918c687..d8640df 100644
--- a/internal/ceres/thread_token_provider.h
+++ b/internal/ceres/thread_token_provider.h
@@ -38,8 +38,7 @@
 #include "ceres/concurrent_queue.h"
 #endif
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 // Helper for C++ thread number identification that is similar to
 // omp_get_thread_num() behaviour. This is necessary to support C++
@@ -91,7 +90,6 @@
   ThreadTokenProvider& operator=(ThreadTokenProvider&) = delete;
 };
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_INTERNAL_THREAD_TOKEN_PROVIDER_H_
diff --git a/internal/ceres/triplet_sparse_matrix.cc b/internal/ceres/triplet_sparse_matrix.cc
index bbb5f67..c1c7ddc 100644
--- a/internal/ceres/triplet_sparse_matrix.cc
+++ b/internal/ceres/triplet_sparse_matrix.cc
@@ -39,8 +39,7 @@
 #include "ceres/types.h"
 #include "glog/logging.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TripletSparseMatrix::TripletSparseMatrix()
     : num_rows_(0), num_cols_(0), max_num_nonzeros_(0), num_nonzeros_(0) {}
@@ -305,5 +304,4 @@
       options.num_rows, options.num_cols, rows, cols, values);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/triplet_sparse_matrix.h b/internal/ceres/triplet_sparse_matrix.h
index 065c690..2cf4290 100644
--- a/internal/ceres/triplet_sparse_matrix.h
+++ b/internal/ceres/triplet_sparse_matrix.h
@@ -40,8 +40,7 @@
 #include "ceres/sparse_matrix.h"
 #include "ceres/types.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 // An implementation of the SparseMatrix interface to store and
 // manipulate sparse matrices in triplet (i,j,s) form.  This object is
@@ -154,8 +153,7 @@
   std::unique_ptr<double[]> values_;
 };
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #include "ceres/internal/reenable_warnings.h"
 
diff --git a/internal/ceres/triplet_sparse_matrix_test.cc b/internal/ceres/triplet_sparse_matrix_test.cc
index 3af634f..e96c994 100644
--- a/internal/ceres/triplet_sparse_matrix_test.cc
+++ b/internal/ceres/triplet_sparse_matrix_test.cc
@@ -34,8 +34,7 @@
 
 #include "gtest/gtest.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TEST(TripletSparseMatrix, DefaultConstructorReturnsEmptyObject) {
   TripletSparseMatrix m;
@@ -344,5 +343,4 @@
   }
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/trust_region_minimizer.cc b/internal/ceres/trust_region_minimizer.cc
index 9ef5167..bf51f96 100644
--- a/internal/ceres/trust_region_minimizer.cc
+++ b/internal/ceres/trust_region_minimizer.cc
@@ -59,8 +59,7 @@
     }                                                            \
   } while (0)
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 void TrustRegionMinimizer::Minimize(const Minimizer::Options& options,
                                     double* parameters,
@@ -821,5 +820,4 @@
   return true;
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/trust_region_minimizer.h b/internal/ceres/trust_region_minimizer.h
index c6fc542..a7b2130 100644
--- a/internal/ceres/trust_region_minimizer.h
+++ b/internal/ceres/trust_region_minimizer.h
@@ -43,8 +43,7 @@
 #include "ceres/trust_region_strategy.h"
 #include "ceres/types.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 // Generic trust region minimization algorithm.
 //
@@ -160,8 +159,7 @@
   int num_consecutive_invalid_steps_;
 };
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #include "ceres/internal/reenable_warnings.h"
 
diff --git a/internal/ceres/trust_region_minimizer_test.cc b/internal/ceres/trust_region_minimizer_test.cc
index 54642d5..ba19356 100644
--- a/internal/ceres/trust_region_minimizer_test.cc
+++ b/internal/ceres/trust_region_minimizer_test.cc
@@ -50,8 +50,7 @@
 #include "ceres/trust_region_strategy.h"
 #include "gtest/gtest.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 // Templated Evaluator for Powell's function. The template parameters
 // indicate which of the four variables/columns of the jacobian are
@@ -433,5 +432,4 @@
   EXPECT_NEAR(expected_final_cost, summary.final_cost, 1e-12);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/trust_region_preprocessor.cc b/internal/ceres/trust_region_preprocessor.cc
index edba47d..4b97021 100644
--- a/internal/ceres/trust_region_preprocessor.cc
+++ b/internal/ceres/trust_region_preprocessor.cc
@@ -48,8 +48,7 @@
 #include "ceres/trust_region_strategy.h"
 #include "ceres/wall_time.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 using std::vector;
 
@@ -391,5 +390,4 @@
   return true;
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/trust_region_preprocessor.h b/internal/ceres/trust_region_preprocessor.h
index 26ef8fa..6b452b8 100644
--- a/internal/ceres/trust_region_preprocessor.h
+++ b/internal/ceres/trust_region_preprocessor.h
@@ -35,8 +35,7 @@
 #include "ceres/internal/export.h"
 #include "ceres/preprocessor.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 class CERES_NO_EXPORT TrustRegionPreprocessor final : public Preprocessor {
  public:
@@ -45,8 +44,7 @@
                   PreprocessedProblem* preprocessed_problem) override;
 };
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #include "ceres/internal/reenable_warnings.h"
 
diff --git a/internal/ceres/trust_region_step_evaluator.cc b/internal/ceres/trust_region_step_evaluator.cc
index 19045ae..90db786 100644
--- a/internal/ceres/trust_region_step_evaluator.cc
+++ b/internal/ceres/trust_region_step_evaluator.cc
@@ -35,8 +35,7 @@
 
 #include "glog/logging.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TrustRegionStepEvaluator::TrustRegionStepEvaluator(
     const double initial_cost, const int max_consecutive_nonmonotonic_steps)
@@ -111,5 +110,4 @@
   }
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/trust_region_step_evaluator.h b/internal/ceres/trust_region_step_evaluator.h
index 8e0c4e9..fee10be 100644
--- a/internal/ceres/trust_region_step_evaluator.h
+++ b/internal/ceres/trust_region_step_evaluator.h
@@ -33,8 +33,7 @@
 
 #include "ceres/internal/export.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 // The job of the TrustRegionStepEvaluator is to evaluate the quality
 // of a step, i.e., how the cost of a step compares with the reduction
@@ -118,7 +117,6 @@
   int num_consecutive_nonmonotonic_steps_;
 };
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_INTERNAL_TRUST_REGION_STEP_EVALUATOR_H_
diff --git a/internal/ceres/trust_region_strategy.cc b/internal/ceres/trust_region_strategy.cc
index 1096cd3..2fa9612 100644
--- a/internal/ceres/trust_region_strategy.cc
+++ b/internal/ceres/trust_region_strategy.cc
@@ -37,8 +37,7 @@
 #include "ceres/dogleg_strategy.h"
 #include "ceres/levenberg_marquardt_strategy.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 TrustRegionStrategy::~TrustRegionStrategy() = default;
 
@@ -59,5 +58,4 @@
   return nullptr;
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/trust_region_strategy.h b/internal/ceres/trust_region_strategy.h
index 33086ca..1b04ceb 100644
--- a/internal/ceres/trust_region_strategy.h
+++ b/internal/ceres/trust_region_strategy.h
@@ -38,8 +38,7 @@
 #include "ceres/internal/export.h"
 #include "ceres/linear_solver.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 class LinearSolver;
 class SparseMatrix;
@@ -141,8 +140,7 @@
   virtual double Radius() const = 0;
 };
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #include "ceres/internal/reenable_warnings.h"
 
diff --git a/internal/ceres/visibility.cc b/internal/ceres/visibility.cc
index f666ce0..2dcfbe7 100644
--- a/internal/ceres/visibility.cc
+++ b/internal/ceres/visibility.cc
@@ -44,8 +44,7 @@
 #include "ceres/pair_hash.h"
 #include "glog/logging.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 using std::make_pair;
 using std::max;
@@ -151,5 +150,4 @@
   return graph;
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/visibility.h b/internal/ceres/visibility.h
index d8f6968..01e34b7 100644
--- a/internal/ceres/visibility.h
+++ b/internal/ceres/visibility.h
@@ -43,8 +43,7 @@
 #include "ceres/internal/disable_warnings.h"
 #include "ceres/internal/export.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 struct CompressedRowBlockStructure;
 
@@ -77,8 +76,7 @@
 CERES_NO_EXPORT std::unique_ptr<WeightedGraph<int>> CreateSchurComplementGraph(
     const std::vector<std::set<int>>& visibility);
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #include "ceres/internal/reenable_warnings.h"
 
diff --git a/internal/ceres/visibility_based_preconditioner.cc b/internal/ceres/visibility_based_preconditioner.cc
index 831a866..e725529 100644
--- a/internal/ceres/visibility_based_preconditioner.cc
+++ b/internal/ceres/visibility_based_preconditioner.cc
@@ -50,8 +50,7 @@
 #include "ceres/visibility.h"
 #include "glog/logging.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 using std::make_pair;
 using std::pair;
@@ -576,5 +575,4 @@
   }
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/visibility_based_preconditioner.h b/internal/ceres/visibility_based_preconditioner.h
index 8079dc3..39bdc9f 100644
--- a/internal/ceres/visibility_based_preconditioner.h
+++ b/internal/ceres/visibility_based_preconditioner.h
@@ -61,8 +61,7 @@
 #include "ceres/preconditioner.h"
 #include "ceres/sparse_cholesky.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 class BlockRandomAccessSparseMatrix;
 class BlockSparseMatrix;
@@ -197,7 +196,6 @@
   std::unique_ptr<SparseCholesky> sparse_cholesky_;
 };
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #endif  // CERES_INTERNAL_VISIBILITY_BASED_PRECONDITIONER_H_
diff --git a/internal/ceres/visibility_based_preconditioner_test.cc b/internal/ceres/visibility_based_preconditioner_test.cc
index 8fcae50..8e0d5fd 100644
--- a/internal/ceres/visibility_based_preconditioner_test.cc
+++ b/internal/ceres/visibility_based_preconditioner_test.cc
@@ -47,8 +47,7 @@
 #include "glog/logging.h"
 #include "gtest/gtest.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 // TODO(sameeragarwal): Re-enable this test once serialization is
 // working again.
@@ -340,5 +339,4 @@
 //   EXPECT_TRUE(PreconditionerValuesMatch());
 // }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/visibility_test.cc b/internal/ceres/visibility_test.cc
index 218bf6e..a107c2f 100644
--- a/internal/ceres/visibility_test.cc
+++ b/internal/ceres/visibility_test.cc
@@ -40,8 +40,7 @@
 #include "glog/logging.h"
 #include "gtest/gtest.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 using std::set;
 using std::vector;
@@ -201,5 +200,4 @@
   }
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/wall_time.cc b/internal/ceres/wall_time.cc
index a54ab64..1a718fb 100644
--- a/internal/ceres/wall_time.cc
+++ b/internal/ceres/wall_time.cc
@@ -44,8 +44,7 @@
 #include <sys/time.h>
 #endif
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 double WallTimeInSeconds() {
 #ifdef CERES_USE_OPENMP
@@ -103,5 +102,4 @@
                 absolute_time_delta);
 }
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
diff --git a/internal/ceres/wall_time.h b/internal/ceres/wall_time.h
index f093eed..36936ee 100644
--- a/internal/ceres/wall_time.h
+++ b/internal/ceres/wall_time.h
@@ -39,8 +39,7 @@
 #include "ceres/stringprintf.h"
 #include "glog/logging.h"
 
-namespace ceres {
-namespace internal {
+namespace ceres::internal {
 
 // Returns time, in seconds, from some arbitrary starting point. If
 // OpenMP is available then the high precision openmp_get_wtime()
@@ -84,8 +83,7 @@
   std::string events_;
 };
 
-}  // namespace internal
-}  // namespace ceres
+}  // namespace ceres::internal
 
 #include "ceres/internal/reenable_warnings.h"