include/ceres/crs_matrix.h

// Ceres Solver - A fast non-linear least squares minimizer
// Copyright 2023 Google Inc. All rights reserved.
// http://ceres-solver.org/
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// Author: sameeragarwal@google.com (Sameer Agarwal)

#ifndef CERES_PUBLIC_CRS_MATRIX_H_
#define CERES_PUBLIC_CRS_MATRIX_H_

#include <vector>

#include "ceres/internal/disable_warnings.h"
#include "ceres/internal/export.h"

namespace ceres {

// A compressed row sparse matrix used primarily for communicating the
// Jacobian matrix to the user.
struct CERES_EXPORT CRSMatrix {
  CRSMatrix() = default;

  int num_rows{0};
  int num_cols{0};

  // A compressed row matrix stores its contents in three arrays,
  // rows, cols and values.
  //
  // rows is a num_rows + 1 sized array that points into the cols and
  // values array. For each row i:
  //
  // cols[rows[i]] ... cols[rows[i + 1] - 1] are the indices of the
  // non-zero columns of row i.
  //
  // values[rows[i]] .. values[rows[i + 1] - 1] are the values of the
  // corresponding entries.
  //
  // cols and values contain as many entries as there are non-zeros in
  // the matrix.
  //
  // e.g, consider the 3x4 sparse matrix
  //
  //  [ 0 10  0  4 ]
  //  [ 0  2 -3  2 ]
  //  [ 1  2  0  0 ]
  //
  // The three arrays will be:
  //
  //
  //            -row0-  ---row1---  -row2-
  //  rows   = [ 0,      2,          5,     7]
  //  cols   = [ 1,  3,  1,  2,  3,  0,  1]
  //  values = [10,  4,  2, -3,  2,  1,  2]

  std::vector<int> cols;
  std::vector<int> rows;
  std::vector<double> values;
};

}  // namespace ceres

#include "ceres/internal/reenable_warnings.h"

#endif  // CERES_PUBLIC_CRS_MATRIX_H_