text: // Ceres Solver - A fast non-linear least squares minimizer
  // Copyright 2013 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)
  
  #include "ceres/block_random_access_diagonal_matrix.h"
  
  #include <algorithm>
  #include <set>
  #include <utility>
  #include <vector>
  #include "Eigen/Dense"
  #include "ceres/internal/port.h"
  #include "ceres/internal/scoped_ptr.h"
  #include "ceres/stl_util.h"
  #include "ceres/triplet_sparse_matrix.h"
  #include "ceres/types.h"
  #include "glog/logging.h"
  
  namespace ceres {
  namespace internal {
  
  using std::vector;
  
  // TODO(sameeragarwal): Drop the dependence on TripletSparseMatrix.
  
  BlockRandomAccessDiagonalMatrix::BlockRandomAccessDiagonalMatrix(
      const vector<int>& blocks)
      : blocks_(blocks) {
    // Build the row/column layout vector and count the number of scalar
    // rows/columns.
    int num_cols = 0;
    int num_nonzeros = 0;
    vector<int> block_positions;
    for (int i = 0; i < blocks_.size(); ++i) {
      block_positions.push_back(num_cols);
      num_cols += blocks_[i];
      num_nonzeros += blocks_[i] * blocks_[i];
    }
  
    VLOG(1) << "Matrix Size [" << num_cols
            << "," << num_cols
            << "] " << num_nonzeros;
  
    tsm_.reset(new TripletSparseMatrix(num_cols, num_cols, num_nonzeros));
    tsm_->set_num_nonzeros(num_nonzeros);
    int* rows = tsm_->mutable_rows();
    int* cols = tsm_->mutable_cols();
    double* values = tsm_->mutable_values();
  
    int pos = 0;
    for (int i = 0; i < blocks_.size(); ++i) {
      const int block_size = blocks_[i];
      layout_.push_back(new CellInfo(values + pos));
      const int block_begin = block_positions[i];
      for (int r = 0; r < block_size; ++r) {
        for (int c = 0; c < block_size; ++c, ++pos) {
          rows[pos] = block_begin + r;
          cols[pos] = block_begin + c;
        }
      }
    }
  }
  
  // Assume that the user does not hold any locks on any cell blocks
  // when they are calling SetZero.
  BlockRandomAccessDiagonalMatrix::~BlockRandomAccessDiagonalMatrix() {
    STLDeleteContainerPointers(layout_.begin(), layout_.end());
  }
  
  CellInfo* BlockRandomAccessDiagonalMatrix::GetCell(int row_block_id,
                                                     int col_block_id,
                                                     int* row,
                                                     int* col,
                                                     int* row_stride,
                                                     int* col_stride) {
    if (row_block_id != col_block_id) {
      return NULL;
    }
    const int stride = blocks_[row_block_id];
  
    // Each cell is stored contiguously as its own little dense matrix.
    *row = 0;
    *col = 0;
    *row_stride = stride;
    *col_stride = stride;
    return layout_[row_block_id];
  }
  
  // Assume that the user does not hold any locks on any cell blocks
  // when they are calling SetZero.
  void BlockRandomAccessDiagonalMatrix::SetZero() {
    if (tsm_->num_nonzeros()) {
      VectorRef(tsm_->mutable_values(),
                tsm_->num_nonzeros()).setZero();
    }
  }
  
  void BlockRandomAccessDiagonalMatrix::Invert() {
    double* values = tsm_->mutable_values();
    for (int i = 0; i < blocks_.size(); ++i) {
      const int block_size = blocks_[i];
      MatrixRef block(values, block_size, block_size);
      block =
          block
          .selfadjointView<Eigen::Upper>()
          .llt()
          .solve(Matrix::Identity(block_size, block_size));
      values += block_size * block_size;
    }
  }
  
  void BlockRandomAccessDiagonalMatrix::RightMultiply(const double* x,
                                                      double* y) const {
    CHECK_NOTNULL(x);
    CHECK_NOTNULL(y);
    const double* values = tsm_->values();
    for (int i = 0; i < blocks_.size(); ++i) {
      const int block_size = blocks_[i];
      ConstMatrixRef block(values, block_size, block_size);
      VectorRef(y, block_size).noalias() += block * ConstVectorRef(x, block_size);
      x += block_size;
      y += block_size;
      values += block_size * block_size;
    }
  }
  
  }  // namespace internal
  }  // namespace ceres
  