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+// Ceres Solver - A fast non-linear least squares minimizer
+// Copyright 2015 Google Inc. All rights reserved.
+// http://ceres-solver.org/
+//
+// 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)
+//
+// Implementation of the SparseMatrix interface for block sparse
+// matrices.
+
+#ifndef CERES_INTERNAL_BLOCK_SPARSE_MATRIX_H_
+#define CERES_INTERNAL_BLOCK_SPARSE_MATRIX_H_
+
+#include <memory>
+#include "ceres/block_structure.h"
+#include "ceres/sparse_matrix.h"
+#include "ceres/internal/eigen.h"
+
+namespace ceres {
+namespace internal {
+
+class TripletSparseMatrix;
+
+// This class implements the SparseMatrix interface for storing and
+// manipulating block sparse matrices. The block structure is stored
+// in the CompressedRowBlockStructure object and one is needed to
+// initialize the matrix. For details on how the blocks structure of
+// the matrix is stored please see the documentation
+//
+//   internal/ceres/block_structure.h
+//
+class BlockSparseMatrix : public SparseMatrix {
+ public:
+  // Construct a block sparse matrix with a fully initialized
+  // CompressedRowBlockStructure objected. The matrix takes over
+  // ownership of this object and destroys it upon destruction.
+  //
+  // TODO(sameeragarwal): Add a function which will validate legal
+  // CompressedRowBlockStructure objects.
+  explicit BlockSparseMatrix(CompressedRowBlockStructure* block_structure);
+
+  BlockSparseMatrix();
+  BlockSparseMatrix(const BlockSparseMatrix&) = delete;
+  void operator=(const BlockSparseMatrix&) = delete;
+
+  virtual ~BlockSparseMatrix();
+
+  // Implementation of SparseMatrix interface.
+  virtual void SetZero();
+  virtual void RightMultiply(const double* x, double* y) const;
+  virtual void LeftMultiply(const double* x, double* y) const;
+  virtual void SquaredColumnNorm(double* x) const;
+  virtual void ScaleColumns(const double* scale);
+  virtual void ToDenseMatrix(Matrix* dense_matrix) const;
+  virtual void ToTextFile(FILE* file) const;
+
+  virtual int num_rows()         const { return num_rows_;     }
+  virtual int num_cols()         const { return num_cols_;     }
+  virtual int num_nonzeros()     const { return num_nonzeros_; }
+  virtual const double* values() const { return values_.get(); }
+  virtual double* mutable_values()     { return values_.get(); }
+
+  void ToTripletSparseMatrix(TripletSparseMatrix* matrix) const;
+  const CompressedRowBlockStructure* block_structure() const;
+
+  // Append the contents of m to the bottom of this matrix. m must
+  // have the same column blocks structure as this matrix.
+  void AppendRows(const BlockSparseMatrix& m);
+
+  // Delete the bottom delta_rows_blocks.
+  void DeleteRowBlocks(int delta_row_blocks);
+
+  static BlockSparseMatrix* CreateDiagonalMatrix(
+      const double* diagonal,
+      const std::vector<Block>& column_blocks);
+
+  struct RandomMatrixOptions {
+    int num_row_blocks = 0;
+    int min_row_block_size = 0;
+    int max_row_block_size = 0;
+    int num_col_blocks = 0;
+    int min_col_block_size = 0;
+    int max_col_block_size = 0;
+
+    // 0 < block_density <= 1 is the probability of a block being
+    // present in the matrix. A given random matrix will not have
+    // precisely this density.
+    double block_density = 0.0;
+
+    // If col_blocks is non-empty, then the generated random matrix
+    // has this block structure and the column related options in this
+    // struct are ignored.
+    std::vector<Block> col_blocks;
+  };
+
+  // Create a random BlockSparseMatrix whose entries are normally
+  // distributed and whose structure is determined by
+  // RandomMatrixOptions.
+  //
+  // Caller owns the result.
+  static BlockSparseMatrix* CreateRandomMatrix(
+      const RandomMatrixOptions& options);
+
+ private:
+  int num_rows_;
+  int num_cols_;
+  int num_nonzeros_;
+  int max_num_nonzeros_;
+  std::unique_ptr<double[]> values_;
+  std::unique_ptr<CompressedRowBlockStructure> block_structure_;
+};
+
+}  // namespace internal
+}  // namespace ceres
+
+#endif  // CERES_INTERNAL_BLOCK_SPARSE_MATRIX_H_