text: // Ceres Solver - A fast non-linear least squares minimizer
  // Copyright 2010, 2011, 2012 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)
  //
  // Interface for matrices that allow block based random access.
  
  #ifndef CERES_INTERNAL_BLOCK_RANDOM_ACCESS_MATRIX_H_
  #define CERES_INTERNAL_BLOCK_RANDOM_ACCESS_MATRIX_H_
  
  #include "ceres/mutex.h"
  
  namespace ceres {
  namespace internal {
  
  // A matrix implementing the BlockRandomAccessMatrix interface is a
  // matrix whose rows and columns are divided into blocks. For example
  // the matrix A:
  //
  //            3     4      5
  //  A =  5 [c_11  c_12  c_13]
  //       4 [c_21  c_22  c_23]
  //
  // has row blocks of size 5 and 4, and column blocks of size 3, 4 and
  // 5. It has six cells corresponding to the six row-column block
  // combinations.
  //
  // BlockRandomAccessMatrix objects provide access to cells c_ij using
  // the GetCell method. when a cell is present, GetCell will return a
  // CellInfo object containing a pointer to an array which contains the
  // cell as a submatrix and a mutex that guards this submatrix. If the
  // user is accessing the matrix concurrently, it is his responsibility
  // to use the mutex to exclude other writers from writing to the cell
  // concurrently.
  //
  // There is no requirement that all cells be present, i.e. the matrix
  // itself can be block sparse. When a cell is not present, the GetCell
  // method will return a NULL pointer.
  //
  // There is no requirement about how the cells are stored beyond that
  // form a dense submatrix of a larger dense matrix. Like everywhere
  // else in Ceres, RowMajor storage assumed.
  //
  // Example usage:
  //
  //  BlockRandomAccessMatrix* A = new BlockRandomAccessMatrixSubClass(...)
  //
  //  int row, col, row_stride, col_stride;
  //  CellInfo* cell = A->GetCell(row_block_id, col_block_id,
  //                              &row, &col,
  //                              &row_stride, &col_stride);
  //
  //  if (cell != NULL) {
  //     MatrixRef m(cell->values, row_stride, col_stride);
  //     CeresMutexLock l(&cell->m);
  //     m.block(row, col, row_block_size, col_block_size) = ...
  //  }
  
  // Structure to carry a pointer to the array containing a cell and the
  // Mutex guarding it.
  struct CellInfo {
    CellInfo()
        : values(NULL) {
    }
  
    explicit CellInfo(double* ptr)
        : values(ptr) {
    }
  
    double* values;
    Mutex m;
  };
  
  class BlockRandomAccessMatrix {
   public:
    virtual ~BlockRandomAccessMatrix();
  
    // If the cell (row_block_id, col_block_id) is present, then return
    // a CellInfo with a pointer to the dense matrix containing it,
    // otherwise return NULL. The dense matrix containing this cell has
    // size row_stride, col_stride and the cell is located at position
    // (row, col) within this matrix.
    //
    // The size of the cell is row_block_size x col_block_size is
    // assumed known to the caller. row_block_size less than or equal to
    // row_stride and col_block_size is upper bounded by col_stride.
    virtual CellInfo* GetCell(int row_block_id,
                              int col_block_id,
                              int* row,
                              int* col,
                              int* row_stride,
                              int* col_stride) = 0;
  
    // Zero out the values of the array. The structure of the matrix
    // (size and sparsity) is preserved.
    virtual void SetZero() = 0;
  
    // Number of scalar rows and columns in the matrix, i.e the sum of
    // all row blocks and column block sizes respectively.
    virtual int num_rows() const = 0;
    virtual int num_cols() const = 0;
  };
  
  }  // namespace internal
  }  // namespace ceres
  
  #endif  // CERES_INTERNAL_BLOCK_RANDOM_ACCESS_MATRIX_H_
  