internal/ceres/block_random_access_sparse_matrix.h

// Ceres Solver - A fast non-linear least squares minimizer
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// Author: sameeragarwal@google.com (Sameer Agarwal)

#ifndef CERES_INTERNAL_BLOCK_RANDOM_ACCESS_SPARSE_MATRIX_H_
#define CERES_INTERNAL_BLOCK_RANDOM_ACCESS_SPARSE_MATRIX_H_

#include <cstdint>
#include <memory>
#include <set>
#include <unordered_map>
#include <utility>
#include <vector>

#include "ceres/block_random_access_matrix.h"
#include "ceres/triplet_sparse_matrix.h"
#include "ceres/internal/port.h"
#include "ceres/types.h"
#include "ceres/small_blas.h"

namespace ceres {
namespace internal {

// A thread safe square block sparse implementation of
// BlockRandomAccessMatrix. Internally a TripletSparseMatrix is used
// for doing the actual storage. This class augments this matrix with
// an unordered_map that allows random read/write access.
class BlockRandomAccessSparseMatrix : public BlockRandomAccessMatrix {
 public:
  // blocks is an array of block sizes. block_pairs is a set of
  // <row_block_id, col_block_id> pairs to identify the non-zero cells
  // of this matrix.
  BlockRandomAccessSparseMatrix(
      const std::vector<int>& blocks,
      const std::set<std::pair<int, int>>& block_pairs);
  BlockRandomAccessSparseMatrix(const BlockRandomAccessSparseMatrix&) = delete;
  void operator=(const BlockRandomAccessSparseMatrix&) = delete;

  // The destructor is not thread safe. It assumes that no one is
  // modifying any cells when the matrix is being destroyed.
  virtual ~BlockRandomAccessSparseMatrix();

  // BlockRandomAccessMatrix Interface.
  CellInfo* GetCell(int row_block_id,
                    int col_block_id,
                    int* row,
                    int* col,
                    int* row_stride,
                    int* col_stride) final;

  // This is not a thread safe method, it assumes that no cell is
  // locked.
  void SetZero() final;

  // Assume that the matrix is symmetric and only one half of the
  // matrix is stored.
  //
  // y += S * x
  void SymmetricRightMultiply(const double* x, double* y) const;

  // Since the matrix is square, num_rows() == num_cols().
  int num_rows() const final { return tsm_->num_rows(); }
  int num_cols() const final { return tsm_->num_cols(); }

  // Access to the underlying matrix object.
  const TripletSparseMatrix* matrix() const { return tsm_.get(); }
  TripletSparseMatrix* mutable_matrix() { return tsm_.get(); }

 private:
  int64_t IntPairToLong(int row, int col) const {
    return row * kMaxRowBlocks + col;
  }

  void LongToIntPair(int64_t index, int* row, int* col) const {
    *row = index / kMaxRowBlocks;
    *col = index % kMaxRowBlocks;
  }

  const int64_t kMaxRowBlocks;

  // row/column block sizes.
  const std::vector<int> blocks_;
  std::vector<int> block_positions_;

  // A mapping from <row_block_id, col_block_id> to the position in
  // the values array of tsm_ where the block is stored.
  typedef std::unordered_map<long int, CellInfo* > LayoutType;
  LayoutType layout_;

  // In order traversal of contents of the matrix. This allows us to
  // implement a matrix-vector which is 20% faster than using the
  // iterator in the Layout object instead.
  std::vector<std::pair<std::pair<int, int>, double*>> cell_values_;
  // The underlying matrix object which actually stores the cells.
  std::unique_ptr<TripletSparseMatrix> tsm_;

  friend class BlockRandomAccessSparseMatrixTest;
};

}  // namespace internal
}  // namespace ceres

#endif  // CERES_INTERNAL_BLOCK_RANDOM_ACCESS_SPARSE_MATRIX_H_