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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)
+
+#ifndef CERES_INTERNAL_TRIPLET_SPARSE_MATRIX_H_
+#define CERES_INTERNAL_TRIPLET_SPARSE_MATRIX_H_
+
+#include <memory>
+#include <vector>
+#include "ceres/sparse_matrix.h"
+#include "ceres/internal/eigen.h"
+#include "ceres/types.h"
+
+namespace ceres {
+namespace internal {
+
+// An implementation of the SparseMatrix interface to store and
+// manipulate sparse matrices in triplet (i,j,s) form.  This object is
+// inspired by the design of the cholmod_triplet struct used in the
+// SuiteSparse package and is memory layout compatible with it.
+class TripletSparseMatrix : public SparseMatrix {
+ public:
+  TripletSparseMatrix();
+  TripletSparseMatrix(int num_rows, int num_cols, int max_num_nonzeros);
+  TripletSparseMatrix(int num_rows,
+                      int num_cols,
+                      const std::vector<int>& rows,
+                      const std::vector<int>& cols,
+                      const std::vector<double>& values);
+
+  explicit TripletSparseMatrix(const TripletSparseMatrix& orig);
+
+  TripletSparseMatrix& operator=(const TripletSparseMatrix& rhs);
+
+  ~TripletSparseMatrix();
+
+  // Implementation of the 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(); }
+  virtual void set_num_nonzeros(int num_nonzeros);
+
+  // Increase max_num_nonzeros and correspondingly increase the size
+  // of rows_, cols_ and values_. If new_max_num_nonzeros is smaller
+  // than max_num_nonzeros_, then num_non_zeros should be less than or
+  // equal to new_max_num_nonzeros, otherwise data loss is possible
+  // and the method crashes.
+  void Reserve(int new_max_num_nonzeros);
+
+  // Append the matrix B at the bottom of this matrix. B should have
+  // the same number of columns as num_cols_.
+  void AppendRows(const TripletSparseMatrix& B);
+
+  // Append the matrix B at the right of this matrix. B should have
+  // the same number of rows as num_rows_;
+  void AppendCols(const TripletSparseMatrix& B);
+
+  // Resize the matrix. Entries which fall outside the new matrix
+  // bounds are dropped and the num_non_zeros changed accordingly.
+  void Resize(int new_num_rows, int new_num_cols);
+
+  int max_num_nonzeros() const { return max_num_nonzeros_; }
+  const int* rows()      const { return rows_.get();       }
+  const int* cols()      const { return cols_.get();       }
+  int* mutable_rows()          { return rows_.get();       }
+  int* mutable_cols()          { return cols_.get();       }
+
+  // Returns true if the entries of the matrix obey the row, column,
+  // and column size bounds and false otherwise.
+  bool AllTripletsWithinBounds() const;
+
+  bool IsValid() const { return AllTripletsWithinBounds(); }
+
+  // Build a sparse diagonal matrix of size num_rows x num_rows from
+  // the array values. Entries of the values array are copied into the
+  // sparse matrix.
+  static TripletSparseMatrix* CreateSparseDiagonalMatrix(const double* values,
+                                                         int num_rows);
+
+  // Options struct to control the generation of random
+  // TripletSparseMatrix objects.
+  struct RandomMatrixOptions {
+    int num_rows;
+    int num_cols;
+    // 0 < density <= 1 is the probability of an entry being
+    // structurally non-zero. A given random matrix will not have
+    // precisely this density.
+    double density;
+  };
+
+  // Create a random CompressedRowSparseMatrix whose entries are
+  // normally distributed and whose structure is determined by
+  // RandomMatrixOptions.
+  //
+  // Caller owns the result.
+  static TripletSparseMatrix* CreateRandomMatrix(
+      const TripletSparseMatrix::RandomMatrixOptions& options);
+
+ private:
+  void AllocateMemory();
+  void CopyData(const TripletSparseMatrix& orig);
+
+  int num_rows_;
+  int num_cols_;
+  int max_num_nonzeros_;
+  int num_nonzeros_;
+
+  // The data is stored as three arrays. For each i, values_[i] is
+  // stored at the location (rows_[i], cols_[i]). If the there are
+  // multiple entries with the same (rows_[i], cols_[i]), the values_
+  // entries corresponding to them are summed up.
+  std::unique_ptr<int[]> rows_;
+  std::unique_ptr<int[]> cols_;
+  std::unique_ptr<double[]> values_;
+};
+
+}  // namespace internal
+}  // namespace ceres
+
+#endif  // CERES_INTERNAL_TRIPLET_SPARSE_MATRIX_H__