Preprocessor for the TrustRegionMinimizer.

1. Base class for preprocessors.
2. A preprocessor for problems that will be solved using
   the trust region minimizer.
3. Added sanity tests to the program reordering options
   for Schur type linear solvers.
4. Tests for the TrustRegionPreprocessor.

Change-Id: I88cd926f0053bbbf2bd6b11e03ec55b8bf473cf1
diff --git a/internal/ceres/CMakeLists.txt b/internal/ceres/CMakeLists.txt
index 4d4f873..5e1fe0f 100644
--- a/internal/ceres/CMakeLists.txt
+++ b/internal/ceres/CMakeLists.txt
@@ -87,6 +87,7 @@
     problem.cc
     problem_impl.cc
     program.cc
+    preprocessor.cc
     reorder_program.cc
     residual_block.cc
     residual_block_utils.cc
@@ -104,6 +105,7 @@
     suitesparse.cc
     summary_utils.cc
     triplet_sparse_matrix.cc
+    trust_region_preprocessor.cc
     trust_region_minimizer.cc
     trust_region_strategy.cc
     types.cc
@@ -289,6 +291,7 @@
   CERES_TEST(symmetric_linear_solver)
   CERES_TEST(triplet_sparse_matrix)
   CERES_TEST(trust_region_minimizer)
+  CERES_TEST(trust_region_preprocessor)
   CERES_TEST(unsymmetric_linear_solver)
   CERES_TEST(visibility)
   CERES_TEST(visibility_based_preconditioner)
diff --git a/internal/ceres/preprocessor.cc b/internal/ceres/preprocessor.cc
new file mode 100644
index 0000000..a572d2b
--- /dev/null
+++ b/internal/ceres/preprocessor.cc
@@ -0,0 +1,111 @@
+// Ceres Solver - A fast non-linear least squares minimizer
+// Copyright 2014 Google Inc. All rights reserved.
+// http://code.google.com/p/ceres-solver/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are met:
+//
+// * Redistributions of source code must retain the above copyright notice,
+//   this list of conditions and the following disclaimer.
+// * Redistributions in binary form must reproduce the above copyright notice,
+//   this list of conditions and the following disclaimer in the documentation
+//   and/or other materials provided with the distribution.
+// * Neither the name of Google Inc. nor the names of its contributors may be
+//   used to endorse or promote products derived from this software without
+//   specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+// ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+// LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+// CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+// SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+// CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+// ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+// POSSIBILITY OF SUCH DAMAGE.
+//
+// Author: sameragarwal@google.com (Sameer Agarwal)
+
+#include "ceres/callbacks.h"
+#include "ceres/gradient_checking_cost_function.h"
+#include "ceres/preprocessor.h"
+#include "ceres/problem_impl.h"
+#include "ceres/solver.h"
+#include "ceres/trust_region_preprocessor.h"
+
+namespace ceres {
+namespace internal {
+
+Preprocessor* Preprocessor::Create(MinimizerType minimizer_type) {
+  if (minimizer_type == TRUST_REGION) {
+    return new TrustRegionPreprocessor;
+  }
+
+  // TODO(sameeragarwal): Add the LineSearchPreprocessor when it is
+  // ready.
+
+  LOG(FATAL) << "Unknown minimizer_type: " << minimizer_type;
+  return NULL;
+}
+
+Preprocessor::~Preprocessor() {
+}
+
+void ChangeNumThreadsIfNeeded(Solver::Options* options) {
+#ifndef CERES_USE_OPENMP
+  if (options->num_threads > 1) {
+    LOG(WARNING)
+        << "OpenMP support is not compiled into this binary; "
+        << "only options.num_threads = 1 is supported. Switching "
+        << "to single threaded mode.";
+    options->num_threads = 1;
+  }
+
+  // Only the Trust Region solver currently uses a linear solver.
+  if (options->minimizer_type == TRUST_REGION &&
+      options->num_linear_solver_threads > 1) {
+    LOG(WARNING)
+        << "OpenMP support is not compiled into this binary; "
+        << "only options.num_linear_solver_threads=1 is supported. Switching "
+        << "to single threaded mode.";
+    options->num_linear_solver_threads = 1;
+  }
+#endif  // CERES_USE_OPENMP
+}
+
+void SetupCommonMinimizerOptions(PreprocessedProblem* pp) {
+  const Solver::Options& options = pp->options;
+  Program* program = pp->reduced_program.get();
+
+  // Assuming that the parameter blocks in the program have been
+  // reordered as needed, extract them into a contiguous vector.
+  pp->reduced_parameters.resize(program->NumParameters());
+  double* reduced_parameters = pp->reduced_parameters.data();
+  program->ParameterBlocksToStateVector(reduced_parameters);
+
+  Minimizer::Options& minimizer_options = pp->minimizer_options;
+  minimizer_options = Minimizer::Options(options);
+  minimizer_options.evaluator = pp->evaluator;
+
+  if (options.logging_type != SILENT) {
+    pp->logging_callback.reset(
+        new LoggingCallback(options.minimizer_type,
+                            options.minimizer_progress_to_stdout));
+    minimizer_options.callbacks.insert(minimizer_options.callbacks.begin(),
+                                       pp->logging_callback.get());
+  }
+
+  if (options.update_state_every_iteration) {
+    pp->state_updating_callback.reset(
+      new StateUpdatingCallback(program, reduced_parameters));
+    // This must get pushed to the front of the callbacks so that it
+    // is run before any of the user callbacks.
+    minimizer_options.callbacks.insert(minimizer_options.callbacks.begin(),
+                                       pp->state_updating_callback.get());
+  }
+}
+
+}  // namespace internal
+}  // namespace ceres
diff --git a/internal/ceres/preprocessor.h b/internal/ceres/preprocessor.h
new file mode 100644
index 0000000..703ba9d
--- /dev/null
+++ b/internal/ceres/preprocessor.h
@@ -0,0 +1,119 @@
+// Ceres Solver - A fast non-linear least squares minimizer
+// Copyright 2014 Google Inc. All rights reserved.
+// http://code.google.com/p/ceres-solver/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are met:
+//
+// * Redistributions of source code must retain the above copyright notice,
+//   this list of conditions and the following disclaimer.
+// * Redistributions in binary form must reproduce the above copyright notice,
+//   this list of conditions and the following disclaimer in the documentation
+//   and/or other materials provided with the distribution.
+// * Neither the name of Google Inc. nor the names of its contributors may be
+//   used to endorse or promote products derived from this software without
+//   specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+// ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+// LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+// CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+// SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+// CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+// ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+// POSSIBILITY OF SUCH DAMAGE.
+//
+// Author: sameragarwal@google.com (Sameer Agarwal)
+
+#ifndef CERES_INTERNAL_PREPROCESSOR_H_
+#define CERES_INTERNAL_PREPROCESSOR_H_
+
+#include "ceres/coordinate_descent_minimizer.h"
+#include "ceres/evaluator.h"
+#include "ceres/internal/eigen.h"
+#include "ceres/internal/port.h"
+#include "ceres/internal/scoped_ptr.h"
+#include "ceres/iteration_callback.h"
+#include "ceres/linear_solver.h"
+#include "ceres/minimizer.h"
+#include "ceres/problem_impl.h"
+#include "ceres/program.h"
+#include "ceres/solver.h"
+
+namespace ceres {
+namespace internal {
+
+struct PreprocessedProblem;
+
+// Given a Problem object and a Solver::Options object indicating the
+// configuration of the solver, the job of the Preprocessor is to
+// analyze the Problem and perform the setup needed to solve it using
+// the desired Minimization algorithm. The setup involves, removing
+// redundancies in the input problem (inactive parameter and residual
+// blocks), finding fill reducing orderings as needed, configuring and
+// creating various objects needed by the Minimizer to solve the
+// problem such as an evaluator, a linear solver etc.
+//
+// Each Minimizer (LineSearchMinimizer and TrustRegionMinimizer) comes
+// with a corresponding Preprocessor (LineSearchPreprocessor and
+// TrustRegionPreprocessor) that knows about its needs and performs
+// the preprocessing needed.
+//
+// The output of the Preprocessor is stored in a PreprocessedProblem
+// object.
+class Preprocessor {
+public:
+  // Factory.
+  static Preprocessor* Create(MinimizerType minimizer_type);
+  virtual ~Preprocessor();
+  virtual bool Preprocess(const Solver::Options& options,
+                          ProblemImpl* problem,
+                          PreprocessedProblem* pp) = 0;
+};
+
+// A PreprocessedProblem is the result of running the Preprocessor on
+// a Problem and Solver::Options object.
+struct PreprocessedProblem {
+  PreprocessedProblem()
+      : fixed_cost(0.0) {
+  }
+
+  string error;
+  Solver::Options options;
+  LinearSolver::Options linear_solver_options;
+  Evaluator::Options evaluator_options;
+  Minimizer::Options minimizer_options;
+
+  ProblemImpl* problem;
+  scoped_ptr<ProblemImpl> gradient_checking_problem;
+  scoped_ptr<Program> reduced_program;
+  scoped_ptr<LinearSolver> linear_solver;
+  scoped_ptr<IterationCallback> logging_callback;
+  scoped_ptr<IterationCallback> state_updating_callback;
+
+  shared_ptr<Evaluator> evaluator;
+  shared_ptr<CoordinateDescentMinimizer> inner_iteration_minimizer;
+
+  vector<double*> removed_parameter_blocks;
+  Vector reduced_parameters;
+  double fixed_cost;
+};
+
+// Common functions used by various preprocessors.
+
+// If OpenMP support is not available and user has requested more than
+// one threads, then set the *_num_threads options as needed to 1.
+void ChangeNumThreadsIfNeeded(Solver::Options* options);
+
+// Extract the effective parameter vector from the preprocessed
+// problem and setup bits of the Minimizer::Options object that are
+// common to all Preprocessors.
+void SetupCommonMinimizerOptions(PreprocessedProblem* pp);
+
+}  // namespace internal
+}  // namespace ceres
+
+#endif  // CERES_INTERNAL_PREPROCESSOR_H_
diff --git a/internal/ceres/reorder_program.cc b/internal/ceres/reorder_program.cc
index 162bfb8..9b40885 100644
--- a/internal/ceres/reorder_program.cc
+++ b/internal/ceres/reorder_program.cc
@@ -313,6 +313,15 @@
     ParameterBlockOrdering* parameter_block_ordering,
     Program* program,
     string* error) {
+  if (parameter_block_ordering->NumElements() != program->NumParameterBlocks()) {
+    *error = StringPrintf(
+        "The program has %d parameter blocks, but the parameter block "
+        "ordering has %d parameter blocks.",
+        program->NumParameterBlocks(),
+        parameter_block_ordering->NumElements());
+    return false;
+  }
+
   if (parameter_block_ordering->NumGroups() == 1) {
     // If the user supplied an parameter_block_ordering with just one
     // group, it is equivalent to the user supplying NULL as an
@@ -340,7 +349,22 @@
     swap(*program->mutable_parameter_blocks(), schur_ordering);
   } else {
     // The user provided an ordering with more than one elimination
-    // group. Trust the user and apply the ordering.
+    // group.
+
+    // Verify that the first elimination group is an independent set.
+    const set<double*>& first_elimination_group =
+        parameter_block_ordering
+        ->group_to_elements()
+        .begin()
+        ->second;
+    if (!program->IsParameterBlockSetIndependent(first_elimination_group)) {
+      *error =
+          StringPrintf("The first elimination group in the parameter block "
+                       "ordering of size %zd is not an independent set",
+                       first_elimination_group.size());
+      return false;
+    }
+
     if (!ApplyOrdering(parameter_map,
                        *parameter_block_ordering,
                        program,
diff --git a/internal/ceres/trust_region_preprocessor.cc b/internal/ceres/trust_region_preprocessor.cc
new file mode 100644
index 0000000..48b58c9
--- /dev/null
+++ b/internal/ceres/trust_region_preprocessor.cc
@@ -0,0 +1,354 @@
+// Ceres Solver - A fast non-linear least squares minimizer
+// Copyright 2014 Google Inc. All rights reserved.
+// http://code.google.com/p/ceres-solver/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are met:
+//
+// * Redistributions of source code must retain the above copyright notice,
+//   this list of conditions and the following disclaimer.
+// * Redistributions in binary form must reproduce the above copyright notice,
+//   this list of conditions and the following disclaimer in the documentation
+//   and/or other materials provided with the distribution.
+// * Neither the name of Google Inc. nor the names of its contributors may be
+//   used to endorse or promote products derived from this software without
+//   specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+// ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+// LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+// CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+// SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+// CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+// ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+// POSSIBILITY OF SUCH DAMAGE.
+//
+// Author: sameeragarwal@google.com (Sameer Agarwal)
+
+#include "ceres/trust_region_preprocessor.h"
+
+#include <numeric>
+#include <string>
+#include "ceres/callbacks.h"
+#include "ceres/evaluator.h"
+#include "ceres/linear_solver.h"
+#include "ceres/minimizer.h"
+#include "ceres/parameter_block.h"
+#include "ceres/preconditioner.h"
+#include "ceres/preprocessor.h"
+#include "ceres/problem_impl.h"
+#include "ceres/program.h"
+#include "ceres/reorder_program.h"
+#include "ceres/suitesparse.h"
+#include "ceres/trust_region_strategy.h"
+#include "ceres/wall_time.h"
+
+namespace ceres {
+namespace internal {
+namespace {
+
+ParameterBlockOrdering* CreateDefaultLinearSolverOrdering(
+    const Program& program) {
+  ParameterBlockOrdering* ordering = new ParameterBlockOrdering;
+  const vector<ParameterBlock*>& parameter_blocks = program.parameter_blocks();
+  for (int i = 0; i < parameter_blocks.size(); ++i) {
+    ordering->AddElementToGroup(
+        const_cast<double*>(parameter_blocks[i]->user_state()), 0);
+  }
+  return ordering;
+}
+
+// Check if all the user supplied values in the parameter blocks are
+// sane or not, and if the program is feasible or not.
+bool IsProgramValid(const Program& program, string* error) {
+  return (program.ParameterBlocksAreFinite(error) &&
+          program.IsFeasible(error));
+}
+
+void AlternateLinearSolverAndPreconditionerForSchurTypeLinearSolver(
+    Solver::Options* options) {
+  if (!IsSchurType(options->linear_solver_type)) {
+    return;
+  }
+
+  const LinearSolverType linear_solver_type_given = options->linear_solver_type;
+  const PreconditionerType preconditioner_type_given =
+      options->preconditioner_type;
+  options->linear_solver_type = LinearSolver::LinearSolverForZeroEBlocks(
+      linear_solver_type_given);
+
+  string message;
+  if (linear_solver_type_given == ITERATIVE_SCHUR) {
+    options->preconditioner_type = Preconditioner::PreconditionerForZeroEBlocks(
+        preconditioner_type_given);
+
+    message =
+        StringPrintf(
+            "No E blocks. Switching from %s(%s) to %s(%s).",
+            LinearSolverTypeToString(linear_solver_type_given),
+            PreconditionerTypeToString(preconditioner_type_given),
+            LinearSolverTypeToString(options->linear_solver_type),
+            PreconditionerTypeToString(options->preconditioner_type));
+  } else {
+    message =
+        StringPrintf(
+            "No E blocks. Switching from %s to %s.",
+            LinearSolverTypeToString(linear_solver_type_given),
+            LinearSolverTypeToString(options->linear_solver_type));
+  }
+
+  VLOG_IF(1, options->logging_type != SILENT) << message;
+}
+
+// For Schur type and SPARSE_NORMAL_CHOLESKY linear solvers, reorder
+// the program to reduce fill-in and increase cache coherency.
+bool ReorderProgram(PreprocessedProblem* pp) {
+  Solver::Options& options = pp->options;
+  if (IsSchurType(options.linear_solver_type)) {
+    return ReorderProgramForSchurTypeLinearSolver(
+        options.linear_solver_type,
+        options.sparse_linear_algebra_library_type,
+        pp->problem->parameter_map(),
+        options.linear_solver_ordering.get(),
+        pp->reduced_program.get(),
+        &pp->error);
+  }
+
+  if (options.linear_solver_type == SPARSE_NORMAL_CHOLESKY &&
+      !options.dynamic_sparsity) {
+    return ReorderProgramForSparseNormalCholesky(
+        options.sparse_linear_algebra_library_type,
+        *options.linear_solver_ordering,
+        pp->reduced_program.get(),
+        &pp->error);
+  }
+
+  return true;
+}
+
+// Configure and create a linear solver object. In doing so, if a
+// sparse direct factorization based linear solver is being used, then
+// find a fill reducing ordering and reorder the program as needed
+// too.
+bool SetupLinearSolver(PreprocessedProblem* pp) {
+  Solver::Options& options = pp->options;
+  if (options.linear_solver_ordering.get() == NULL) {
+    // If the user has not supplied a linear solver ordering, then we
+    // assume that they are giving all the freedom to us in choosing
+    // the best possible ordering. This intent can be indicated by
+    // putting all the parameter block in the same elimination group.
+    options.linear_solver_ordering.reset(
+        CreateDefaultLinearSolverOrdering(*pp->reduced_program));
+  } else {
+    // If the user supplied an ordering, then check if the first
+    // elimination group is still non-empty after the reduced problem
+    // has been constructed.
+    //
+    // This is important for Schur type linear solvers, where the
+    // first elimination group is special -- it needs to be an
+    // independent set.
+    //
+    // If the first elimination group is empty, then we cannot use the
+    // user's requested linear solver (and a preconditioner as the
+    // case may be) so we must use a different one.
+    ParameterBlockOrdering* ordering = options.linear_solver_ordering.get();
+    const int min_group_id = ordering->MinNonZeroGroup();
+    ordering->Remove(pp->removed_parameter_blocks);
+    if (IsSchurType(options.linear_solver_type) &&
+        min_group_id != ordering->MinNonZeroGroup()) {
+      AlternateLinearSolverAndPreconditionerForSchurTypeLinearSolver(
+          &options);
+    }
+  }
+
+  // Reorder the program to reduce fill in and improve cache coherency
+  // of the Jacobian.
+  if (!ReorderProgram(pp)) {
+    return false;
+  }
+
+  // Configure the linear solver.
+  pp->linear_solver_options = LinearSolver::Options();
+  pp->linear_solver_options.min_num_iterations =
+      options.min_linear_solver_iterations;
+  pp->linear_solver_options.max_num_iterations =
+      options.max_linear_solver_iterations;
+  pp->linear_solver_options.type = options.linear_solver_type;
+  pp->linear_solver_options.preconditioner_type = options.preconditioner_type;
+  pp->linear_solver_options.visibility_clustering_type =
+      options.visibility_clustering_type;
+  pp->linear_solver_options.sparse_linear_algebra_library_type =
+      options.sparse_linear_algebra_library_type;
+  pp->linear_solver_options.dense_linear_algebra_library_type =
+      options.dense_linear_algebra_library_type;
+  pp->linear_solver_options.dynamic_sparsity = options.dynamic_sparsity;
+  pp->linear_solver_options.num_threads = options.num_linear_solver_threads;
+
+  // Ignore user's postordering preferences and force it to be true if
+  // cholmod_camd is not available. This ensures that the linear
+  // solver does not assume that a fill-reducing pre-ordering has been
+  // done.
+  pp->linear_solver_options.use_postordering = options.use_postordering;
+  if (options.linear_solver_type == SPARSE_SCHUR &&
+      options.sparse_linear_algebra_library_type == SUITE_SPARSE &&
+      !SuiteSparse::IsConstrainedApproximateMinimumDegreeOrderingAvailable()) {
+    pp->linear_solver_options.use_postordering = true;
+  }
+
+  OrderingToGroupSizes(options.linear_solver_ordering.get(),
+                       &pp->linear_solver_options.elimination_groups);
+
+  // Schur type solvers expect at least two elimination groups. If
+  // there is only one elimination group, then it is guaranteed that
+  // this group only contains e_blocks. Thus we add a dummy
+  // elimination group with zero blocks in it.
+  if (IsSchurType(pp->linear_solver_options.type) &&
+      pp->linear_solver_options.elimination_groups.size() == 1) {
+    pp->linear_solver_options.elimination_groups.push_back(0);
+  }
+
+  pp->linear_solver.reset(LinearSolver::Create(pp->linear_solver_options));
+  return (pp->linear_solver.get() != NULL);
+}
+
+// Configure and create the evaluator.
+bool SetupEvaluator(PreprocessedProblem* pp) {
+  const Solver::Options& options = pp->options;
+  pp->evaluator_options = Evaluator::Options();
+  pp->evaluator_options.linear_solver_type = options.linear_solver_type;
+  pp->evaluator_options.num_eliminate_blocks = 0;
+  if (IsSchurType(options.linear_solver_type)) {
+    pp->evaluator_options.num_eliminate_blocks =
+        options
+        .linear_solver_ordering
+        ->group_to_elements().begin()
+        ->second.size();
+  }
+
+  pp->evaluator_options.num_threads = options.num_threads;
+  pp->evaluator_options.dynamic_sparsity = options.dynamic_sparsity;
+  pp->evaluator.reset(Evaluator::Create(pp->evaluator_options,
+                                        pp->reduced_program.get(),
+                                        &pp->error));
+
+  return (pp->evaluator.get() != NULL);
+}
+
+// If the user requested inner iterations, then find an inner
+// iteration ordering as needed and configure and create a
+// CoordinateDescentMinimizer object to perform the inner iterations.
+bool SetupInnerIterationMinimizer(PreprocessedProblem* pp) {
+  Solver::Options& options = pp->options;
+  if (!options.use_inner_iterations) {
+    return true;
+  }
+
+  // With just one parameter block, the outer iteration of the trust
+  // region method and inner iterations are doing exactly the same
+  // thing, and thus inner iterations are not needed.
+  if (pp->reduced_program->NumParameterBlocks() == 1) {
+    LOG(WARNING) << "Reduced problem only contains one parameter block."
+                 << "Disabling inner iterations.";
+    return true;
+  }
+
+  if (options.inner_iteration_ordering.get() != NULL) {
+    // If the user supplied an ordering, then remove the set of
+    // inactive parameter blocks from it
+    options.inner_iteration_ordering->Remove(pp->removed_parameter_blocks);
+    if (options.inner_iteration_ordering->NumElements() == 0) {
+      LOG(WARNING) << "No remaining elements in the inner iteration ordering.";
+      return true;
+    }
+
+    // Validate the reduced ordering.
+    if (!CoordinateDescentMinimizer::IsOrderingValid(
+            *pp->reduced_program,
+            *options.inner_iteration_ordering,
+            &pp->error)) {
+      return false;
+    }
+  } else {
+    // The user did not supply an ordering, so create one.
+    options.inner_iteration_ordering.reset(
+        CoordinateDescentMinimizer::CreateOrdering(*pp->reduced_program));
+  }
+
+  pp->inner_iteration_minimizer.reset(new CoordinateDescentMinimizer);
+  return pp->inner_iteration_minimizer->Init(*pp->reduced_program,
+                                             pp->problem->parameter_map(),
+                                             *options.inner_iteration_ordering,
+                                             &pp->error);
+}
+
+// Configure and create a TrustRegionMinimizer object.
+void SetupMinimizerOptions(PreprocessedProblem* pp) {
+  const Solver::Options& options = pp->options;
+
+  SetupCommonMinimizerOptions(pp);
+  pp->minimizer_options.jacobian.reset(pp->evaluator->CreateJacobian());
+  pp->minimizer_options.inner_iteration_minimizer =
+      pp->inner_iteration_minimizer;
+
+  TrustRegionStrategy::Options strategy_options;
+  strategy_options.linear_solver = pp->linear_solver.get();
+  strategy_options.initial_radius =
+      options.initial_trust_region_radius;
+  strategy_options.max_radius = options.max_trust_region_radius;
+  strategy_options.min_lm_diagonal = options.min_lm_diagonal;
+  strategy_options.max_lm_diagonal = options.max_lm_diagonal;
+  strategy_options.trust_region_strategy_type =
+      options.trust_region_strategy_type;
+  strategy_options.dogleg_type = options.dogleg_type;
+  pp->minimizer_options.trust_region_strategy.reset(
+      CHECK_NOTNULL(TrustRegionStrategy::Create(strategy_options)));
+}
+
+}  // namespace
+
+TrustRegionPreprocessor::~TrustRegionPreprocessor() {
+}
+
+bool TrustRegionPreprocessor::Preprocess(const Solver::Options& options,
+                                         ProblemImpl* problem,
+                                         PreprocessedProblem* pp) {
+  CHECK_NOTNULL(pp);
+  pp->options = options;
+  ChangeNumThreadsIfNeeded(&pp->options);
+
+  pp->problem = problem;
+  Program* program = problem->mutable_program();
+  if (!IsProgramValid(*program, &pp->error)) {
+    return false;
+  }
+
+  pp->reduced_program.reset(
+      program->CreateReducedProgram(&pp->removed_parameter_blocks,
+                                    &pp->fixed_cost,
+                                    &pp->error));
+
+  if (pp->reduced_program.get() == NULL) {
+    return false;
+  }
+
+  if (pp->reduced_program->NumParameterBlocks() == 0) {
+    // The reduced problem has no parameter or residual blocks. There
+    // is nothing more to do.
+    return true;
+  }
+
+  if (!SetupLinearSolver(pp) ||
+      !SetupEvaluator(pp) ||
+      !SetupInnerIterationMinimizer(pp)) {
+    return false;
+  }
+
+  SetupMinimizerOptions(pp);
+  return true;
+}
+
+}  // namespace internal
+}  // namespace ceres
diff --git a/internal/ceres/trust_region_preprocessor.h b/internal/ceres/trust_region_preprocessor.h
new file mode 100644
index 0000000..ba70ff9
--- /dev/null
+++ b/internal/ceres/trust_region_preprocessor.h
@@ -0,0 +1,50 @@
+// Ceres Solver - A fast non-linear least squares minimizer
+// Copyright 2014 Google Inc. All rights reserved.
+// http://code.google.com/p/ceres-solver/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are met:
+//
+// * Redistributions of source code must retain the above copyright notice,
+//   this list of conditions and the following disclaimer.
+// * Redistributions in binary form must reproduce the above copyright notice,
+//   this list of conditions and the following disclaimer in the documentation
+//   and/or other materials provided with the distribution.
+// * Neither the name of Google Inc. nor the names of its contributors may be
+//   used to endorse or promote products derived from this software without
+//   specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+// ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+// LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+// CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+// SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+// CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+// ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+// POSSIBILITY OF SUCH DAMAGE.
+//
+// Author: sameragarwal@google.com (Sameer Agarwal)
+
+#ifndef CERES_INTERNAL_TRUST_REGION_PREPROCESSOR_H_
+#define CERES_INTERNAL_TRUST_REGION_PREPROCESSOR_H_
+
+#include "ceres/preprocessor.h"
+
+namespace ceres {
+namespace internal {
+
+class TrustRegionPreprocessor : public Preprocessor {
+ public:
+  virtual ~TrustRegionPreprocessor();
+  virtual bool Preprocess(const Solver::Options& options,
+                          ProblemImpl* problem,
+                          PreprocessedProblem* preprocessed_problem);
+};
+
+}  // namespace internal
+}  // namespace ceres
+
+#endif  // CERES_INTERNAL_TRUST_REGION_PREPROCESSOR_H_
diff --git a/internal/ceres/trust_region_preprocessor_test.cc b/internal/ceres/trust_region_preprocessor_test.cc
new file mode 100644
index 0000000..cfa22fe
--- /dev/null
+++ b/internal/ceres/trust_region_preprocessor_test.cc
@@ -0,0 +1,399 @@
+// Ceres Solver - A fast non-linear least squares minimizer
+// Copyright 2014 Google Inc. All rights reserved.
+// http://code.google.com/p/ceres-solver/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are met:
+//
+// * Redistributions of source code must retain the above copyright notice,
+//   this list of conditions and the following disclaimer.
+// * Redistributions in binary form must reproduce the above copyright notice,
+//   this list of conditions and the following disclaimer in the documentation
+//   and/or other materials provided with the distribution.
+// * Neither the name of Google Inc. nor the names of its contributors may be
+//   used to endorse or promote products derived from this software without
+//   specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+// ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+// LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+// CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+// SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+// CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+// ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+// POSSIBILITY OF SUCH DAMAGE.
+//
+// Author: sameeragarwal@google.com (Sameer Agarwal)
+
+#include <map>
+
+#include "ceres/ordered_groups.h"
+#include "ceres/problem_impl.h"
+#include "ceres/sized_cost_function.h"
+#include "ceres/solver.h"
+#include "ceres/trust_region_preprocessor.h"
+#include "gtest/gtest.h"
+
+namespace ceres {
+namespace internal {
+
+TEST(TrustRegionPreprocessor, ZeroProblem) {
+  ProblemImpl problem;
+  Solver::Options options;
+  TrustRegionPreprocessor preprocessor;
+  PreprocessedProblem pp;
+  EXPECT_TRUE(preprocessor.Preprocess(options, &problem, &pp));
+}
+
+TEST(TrustRegionPreprocessor, ProblemWithInvalidParameterBlock) {
+  ProblemImpl problem;
+  double x = 1.0/0.0;
+  problem.AddParameterBlock(&x, 1);
+  Solver::Options options;
+  TrustRegionPreprocessor preprocessor;
+  PreprocessedProblem pp;
+  EXPECT_FALSE(preprocessor.Preprocess(options, &problem, &pp));
+}
+
+TEST(TrustRegionPreprocessor, ParameterBlockBoundsAreInvalid) {
+  ProblemImpl problem;
+  double x = 1.0;
+  problem.AddParameterBlock(&x, 1);
+  problem.SetParameterUpperBound(&x, 0, 1.0);
+  problem.SetParameterLowerBound(&x, 0, 2.0);
+  Solver::Options options;
+  TrustRegionPreprocessor preprocessor;
+  PreprocessedProblem pp;
+  EXPECT_FALSE(preprocessor.Preprocess(options, &problem, &pp));
+}
+
+TEST(TrustRegionPreprocessor, ParamterBlockIsInfeasible) {
+  ProblemImpl problem;
+  double x = 3.0;
+  problem.AddParameterBlock(&x, 1);
+  problem.SetParameterUpperBound(&x, 0, 1.0);
+  problem.SetParameterLowerBound(&x, 0, 2.0);
+  problem.SetParameterBlockConstant(&x);
+  Solver::Options options;
+  TrustRegionPreprocessor preprocessor;
+  PreprocessedProblem pp;
+  EXPECT_FALSE(preprocessor.Preprocess(options, &problem, &pp));
+}
+
+class FailingCostFunction : public SizedCostFunction<1, 1> {
+ public:
+  bool Evaluate(double const* const* parameters,
+                double* residuals,
+                double** jacobians) const {
+    return false;
+  }
+};
+
+TEST(TrustRegionPreprocessor, RemoveParameterBlocksFailed) {
+  ProblemImpl problem;
+  double x = 3.0;
+  problem.AddResidualBlock(new FailingCostFunction, NULL, &x);
+  problem.SetParameterBlockConstant(&x);
+   Solver::Options options;
+  TrustRegionPreprocessor preprocessor;
+  PreprocessedProblem pp;
+  EXPECT_FALSE(preprocessor.Preprocess(options, &problem, &pp));
+}
+
+TEST(TrustRegionPreprocessor, RemoveParameterBlocksSucceeds) {
+  ProblemImpl problem;
+  double x = 3.0;
+  problem.AddParameterBlock(&x, 1);
+  Solver::Options options;
+  TrustRegionPreprocessor preprocessor;
+  PreprocessedProblem pp;
+  EXPECT_TRUE(preprocessor.Preprocess(options, &problem, &pp));
+}
+
+template<int kNumResiduals, int N1 = 0, int N2 = 0, int N3 = 0>
+class DummyCostFunction : public SizedCostFunction<kNumResiduals, N1, N2, N3> {
+ public:
+  bool Evaluate(double const* const* parameters,
+                double* residuals,
+                double** jacobians) const {
+    for (int i = 0; i < kNumResiduals; ++i) {
+      residuals[i] = kNumResiduals * kNumResiduals + i;
+    }
+
+    if (jacobians == NULL) {
+      return true;
+    }
+
+    if (jacobians[0] != NULL) {
+      MatrixRef j(jacobians[0], kNumResiduals, N1);
+      j.setOnes();
+      j *= kNumResiduals * N1;
+    }
+
+    if (N2 == 0) {
+      return true;
+    }
+
+    if (jacobians[1] != NULL) {
+      MatrixRef j(jacobians[1], kNumResiduals, N2);
+      j.setOnes();
+      j *= kNumResiduals * N2;
+    }
+
+    if (N3 == 0) {
+      return true;
+    }
+
+    if (jacobians[2] != NULL) {
+      MatrixRef j(jacobians[2], kNumResiduals, N3);
+      j.setOnes();
+      j *= kNumResiduals * N3;
+    }
+
+    return true;
+  }
+};
+
+class LinearSolverAndEvaluatorCreationTest : public ::testing::Test {
+ public:
+  virtual void SetUp() {
+    x_ = 1.0;
+    y_ = 1.0;
+    z_ = 1.0;
+    problem_.AddResidualBlock(new DummyCostFunction<1, 1, 1>, NULL, &x_, &y_);
+    problem_.AddResidualBlock(new DummyCostFunction<1, 1, 1>, NULL, &y_, &z_);
+  }
+
+  void Run(const LinearSolverType linear_solver_type) {
+    Solver::Options options;
+    options.linear_solver_type = linear_solver_type;
+    TrustRegionPreprocessor preprocessor;
+    PreprocessedProblem pp;
+    EXPECT_TRUE(preprocessor.Preprocess(options, &problem_, &pp));
+    EXPECT_EQ(pp.options.linear_solver_type, linear_solver_type);
+    EXPECT_EQ(pp.linear_solver_options.type, linear_solver_type);
+    EXPECT_EQ(pp.evaluator_options.linear_solver_type, linear_solver_type);
+    EXPECT_TRUE(pp.linear_solver.get() != NULL);
+    EXPECT_TRUE(pp.evaluator.get() != NULL);
+  }
+
+ protected:
+  ProblemImpl problem_;
+  double x_;
+  double y_;
+  double z_;
+};
+
+TEST_F(LinearSolverAndEvaluatorCreationTest, DenseQR) {
+  Run(DENSE_QR);
+}
+
+TEST_F(LinearSolverAndEvaluatorCreationTest, DenseNormalCholesky) {
+  Run(DENSE_NORMAL_CHOLESKY);
+}
+
+TEST_F(LinearSolverAndEvaluatorCreationTest, DenseSchur) {
+  Run(DENSE_SCHUR);
+}
+
+#if defined(CERES_USE_EIGEN_SPARSE) || !defined(CERES_NO_SUITE_SPARSE) || !defined(CERES_NO_CX_SPARSE)
+TEST_F(LinearSolverAndEvaluatorCreationTest, SparseNormalCholesky) {
+  Run(SPARSE_NORMAL_CHOLESKY);
+}
+#endif
+
+#if defined(CERES_USE_EIGEN_SPARSE) || !defined(CERES_NO_SUITE_SPARSE) || !defined(CERES_NO_CX_SPARSE)
+TEST_F(LinearSolverAndEvaluatorCreationTest, SparseSchur) {
+  Run(SPARSE_SCHUR);
+}
+#endif
+
+TEST_F(LinearSolverAndEvaluatorCreationTest, CGNR) {
+  Run(CGNR);
+}
+
+TEST_F(LinearSolverAndEvaluatorCreationTest, IterativeSchur) {
+  Run(ITERATIVE_SCHUR);
+}
+
+TEST(TrustRegionPreprocessor, SchurTypeSolverWithBadOrdering) {
+  ProblemImpl problem;
+  double x = 1.0;
+  double y = 1.0;
+  double z = 1.0;
+  problem.AddResidualBlock(new DummyCostFunction<1, 1, 1>, NULL, &x, &y);
+  problem.AddResidualBlock(new DummyCostFunction<1, 1, 1>, NULL, &y, &z);
+
+  Solver::Options options;
+  options.linear_solver_type = DENSE_SCHUR;
+  options.linear_solver_ordering.reset(new ParameterBlockOrdering);
+  options.linear_solver_ordering->AddElementToGroup(&x, 0);
+  options.linear_solver_ordering->AddElementToGroup(&y, 0);
+  options.linear_solver_ordering->AddElementToGroup(&z, 1);
+
+  TrustRegionPreprocessor preprocessor;
+  PreprocessedProblem pp;
+  EXPECT_FALSE(preprocessor.Preprocess(options, &problem, &pp));
+}
+
+TEST(TrustRegionPreprocessor, SchurTypeSolverWithGoodOrdering) {
+  ProblemImpl problem;
+  double x = 1.0;
+  double y = 1.0;
+  double z = 1.0;
+  problem.AddResidualBlock(new DummyCostFunction<1, 1, 1>, NULL, &x, &y);
+  problem.AddResidualBlock(new DummyCostFunction<1, 1, 1>, NULL, &y, &z);
+
+  Solver::Options options;
+  options.linear_solver_type = DENSE_SCHUR;
+  options.linear_solver_ordering.reset(new ParameterBlockOrdering);
+  options.linear_solver_ordering->AddElementToGroup(&x, 0);
+  options.linear_solver_ordering->AddElementToGroup(&z, 0);
+  options.linear_solver_ordering->AddElementToGroup(&y, 1);
+
+  TrustRegionPreprocessor preprocessor;
+  PreprocessedProblem pp;
+  EXPECT_TRUE(preprocessor.Preprocess(options, &problem, &pp));
+  EXPECT_EQ(pp.options.linear_solver_type, DENSE_SCHUR);
+  EXPECT_EQ(pp.linear_solver_options.type, DENSE_SCHUR);
+  EXPECT_EQ(pp.evaluator_options.linear_solver_type, DENSE_SCHUR);
+  EXPECT_TRUE(pp.linear_solver.get() != NULL);
+  EXPECT_TRUE(pp.evaluator.get() != NULL);
+}
+
+TEST(TrustRegionPreprocessor, SchurTypeSolverWithEmptyFirstEliminationGroup) {
+  ProblemImpl problem;
+  double x = 1.0;
+  double y = 1.0;
+  double z = 1.0;
+  problem.AddResidualBlock(new DummyCostFunction<1, 1, 1>, NULL, &x, &y);
+  problem.AddResidualBlock(new DummyCostFunction<1, 1, 1>, NULL, &y, &z);
+  problem.SetParameterBlockConstant(&x);
+  problem.SetParameterBlockConstant(&z);
+
+  Solver::Options options;
+  options.linear_solver_type = DENSE_SCHUR;
+  options.linear_solver_ordering.reset(new ParameterBlockOrdering);
+  options.linear_solver_ordering->AddElementToGroup(&x, 0);
+  options.linear_solver_ordering->AddElementToGroup(&z, 0);
+  options.linear_solver_ordering->AddElementToGroup(&y, 1);
+
+  TrustRegionPreprocessor preprocessor;
+  PreprocessedProblem pp;
+  EXPECT_TRUE(preprocessor.Preprocess(options, &problem, &pp));
+  EXPECT_EQ(pp.options.linear_solver_type, DENSE_QR);
+  EXPECT_EQ(pp.linear_solver_options.type, DENSE_QR);
+  EXPECT_EQ(pp.evaluator_options.linear_solver_type, DENSE_QR);
+  EXPECT_TRUE(pp.linear_solver.get() != NULL);
+  EXPECT_TRUE(pp.evaluator.get() != NULL);
+}
+
+TEST(TrustRegionPreprocessor, SchurTypeSolverWithEmptySecondEliminationGroup) {
+  ProblemImpl problem;
+  double x = 1.0;
+  double y = 1.0;
+  double z = 1.0;
+  problem.AddResidualBlock(new DummyCostFunction<1, 1, 1>, NULL, &x, &y);
+  problem.AddResidualBlock(new DummyCostFunction<1, 1, 1>, NULL, &y, &z);
+  problem.SetParameterBlockConstant(&y);
+
+  Solver::Options options;
+  options.linear_solver_type = DENSE_SCHUR;
+  options.linear_solver_ordering.reset(new ParameterBlockOrdering);
+  options.linear_solver_ordering->AddElementToGroup(&x, 0);
+  options.linear_solver_ordering->AddElementToGroup(&z, 0);
+  options.linear_solver_ordering->AddElementToGroup(&y, 1);
+
+  TrustRegionPreprocessor preprocessor;
+  PreprocessedProblem pp;
+  EXPECT_TRUE(preprocessor.Preprocess(options, &problem, &pp));
+  EXPECT_EQ(pp.options.linear_solver_type, DENSE_SCHUR);
+  EXPECT_EQ(pp.linear_solver_options.type, DENSE_SCHUR);
+  EXPECT_EQ(pp.evaluator_options.linear_solver_type, DENSE_SCHUR);
+  EXPECT_TRUE(pp.linear_solver.get() != NULL);
+  EXPECT_TRUE(pp.evaluator.get() != NULL);
+}
+
+TEST(TrustRegionProcessor, InnerIterationsWithOneParameterBlock) {
+  ProblemImpl problem;
+  double x = 1.0;
+  problem.AddResidualBlock(new DummyCostFunction<1, 1>, NULL, &x);
+
+  Solver::Options options;
+  options.use_inner_iterations = true;
+
+  TrustRegionPreprocessor preprocessor;
+  PreprocessedProblem pp;
+  EXPECT_TRUE(preprocessor.Preprocess(options, &problem, &pp));
+  EXPECT_TRUE(pp.linear_solver.get() != NULL);
+  EXPECT_TRUE(pp.evaluator.get() != NULL);
+  EXPECT_TRUE(pp.inner_iteration_minimizer.get() == NULL);
+}
+
+TEST(TrustRegionProcessor, InnerIterationsWithTwoParameterBlocks) {
+  ProblemImpl problem;
+  double x = 1.0;
+  double y = 1.0;
+  double z = 1.0;
+  problem.AddResidualBlock(new DummyCostFunction<1, 1, 1>, NULL, &x, &y);
+  problem.AddResidualBlock(new DummyCostFunction<1, 1, 1>, NULL, &y, &z);
+
+  Solver::Options options;
+  options.use_inner_iterations = true;
+
+  TrustRegionPreprocessor preprocessor;
+  PreprocessedProblem pp;
+  EXPECT_TRUE(preprocessor.Preprocess(options, &problem, &pp));
+  EXPECT_TRUE(pp.linear_solver.get() != NULL);
+  EXPECT_TRUE(pp.evaluator.get() != NULL);
+  EXPECT_TRUE(pp.inner_iteration_minimizer.get() != NULL);
+}
+
+TEST(TrustRegionProcessor, InvalidInnerIterationsOrdering) {
+  ProblemImpl problem;
+  double x = 1.0;
+  double y = 1.0;
+  double z = 1.0;
+  problem.AddResidualBlock(new DummyCostFunction<1, 1, 1>, NULL, &x, &y);
+  problem.AddResidualBlock(new DummyCostFunction<1, 1, 1>, NULL, &y, &z);
+
+  Solver::Options options;
+  options.use_inner_iterations = true;
+  options.inner_iteration_ordering.reset(new ParameterBlockOrdering);
+  options.inner_iteration_ordering->AddElementToGroup(&x, 0);
+  options.inner_iteration_ordering->AddElementToGroup(&z, 0);
+  options.inner_iteration_ordering->AddElementToGroup(&y, 0);
+
+  TrustRegionPreprocessor preprocessor;
+  PreprocessedProblem pp;
+  EXPECT_FALSE(preprocessor.Preprocess(options, &problem, &pp));
+}
+
+TEST(TrustRegionProcessor, ValidInnerIterationsOrdering) {
+  ProblemImpl problem;
+  double x = 1.0;
+  double y = 1.0;
+  double z = 1.0;
+  problem.AddResidualBlock(new DummyCostFunction<1, 1, 1>, NULL, &x, &y);
+  problem.AddResidualBlock(new DummyCostFunction<1, 1, 1>, NULL, &y, &z);
+
+  Solver::Options options;
+  options.use_inner_iterations = true;
+  options.inner_iteration_ordering.reset(new ParameterBlockOrdering);
+  options.inner_iteration_ordering->AddElementToGroup(&x, 0);
+  options.inner_iteration_ordering->AddElementToGroup(&z, 0);
+  options.inner_iteration_ordering->AddElementToGroup(&y, 1);
+
+  TrustRegionPreprocessor preprocessor;
+  PreprocessedProblem pp;
+  EXPECT_TRUE(preprocessor.Preprocess(options, &problem, &pp));
+  EXPECT_TRUE(pp.linear_solver.get() != NULL);
+  EXPECT_TRUE(pp.evaluator.get() != NULL);
+  EXPECT_TRUE(pp.inner_iteration_minimizer.get() != NULL);
+}
+
+}  // namespace internal
+}  // namespace ceres