text: // g2o - General Graph Optimization
  // Copyright (C) 2011 R. Kuemmerle, G. Grisetti, W. Burgard
  // All rights reserved.
  //
  // Redistribution and use in source and binary forms, with or without
  // modification, are permitted provided that the following conditions are
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  //
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  #ifndef G2O_SPARSE_BLOCK_MATRIX_DIAGONAL_H
  #define G2O_SPARSE_BLOCK_MATRIX_DIAGONAL_H
  
  #include <vector>
  #include <Eigen/Core>
  #include <Eigen/StdVector>
  
  #include "g2o/config.h"
  #include "matrix_operations.h"
  
  namespace g2o {
  
    /**
     * \brief Sparse matrix which uses blocks on the diagonal
     *
     * This class is used as a const view on a SparseBlockMatrix
     * which allows a faster iteration over the elements of the
     * matrix.
     */
    template <class MatrixType>
    class SparseBlockMatrixDiagonal
    {
      public:
        //! this is the type of the elementary block, it is an Eigen::Matrix.
        typedef MatrixType SparseMatrixBlock;
  
        //! columns of the matrix
        int cols() const {return _blockIndices.size() ? _blockIndices.back() : 0;}
        //! rows of the matrix
        int rows() const {return _blockIndices.size() ? _blockIndices.back() : 0;}
  
        typedef std::vector<MatrixType, Eigen::aligned_allocator<MatrixType> >      DiagonalVector;
  
        SparseBlockMatrixDiagonal(const std::vector<int>& blockIndices) :
          _blockIndices(blockIndices)
        {}
  
        //! how many rows/cols does the block at block-row / block-column r has?
        inline int dimOfBlock(int r) const { return r ? _blockIndices[r] - _blockIndices[r-1] : _blockIndices[0] ; }
  
        //! where does the row /col at block-row / block-column r starts?
        inline int baseOfBlock(int r) const { return r ? _blockIndices[r-1] : 0 ; }
  
        //! the block matrices per block-column
        const DiagonalVector& diagonal() const { return _diagonal;}
        DiagonalVector& diagonal() { return _diagonal;}
  
        //! indices of the row blocks
        const std::vector<int>& blockIndices() const { return _blockIndices;}
  
        void multiply(double*& dest, const double* src) const
        {
          int destSize=cols();
          if (! dest) {
            dest=new double[destSize];
            memset(dest,0, destSize*sizeof(double));
          }
  
          // map the memory by Eigen
          Eigen::Map<Eigen::VectorXd> destVec(dest, destSize);
          Eigen::Map<const Eigen::VectorXd> srcVec(src, rows());
  
  #      ifdef G2O_OPENMP
  #      pragma omp parallel for default (shared) schedule(dynamic, 10)
  #      endif
          for (int i=0; i < static_cast<int>(_diagonal.size()); ++i){
            int destOffset = baseOfBlock(i);
            int srcOffset = destOffset;
            const SparseMatrixBlock& A = _diagonal[i];
            // destVec += *A.transpose() * srcVec (according to the sub-vector parts)
            internal::template axpy<SparseMatrixBlock>(A, srcVec, srcOffset, destVec, destOffset);
          }
        }
  
      protected:
        const std::vector<int>& _blockIndices; ///< vector of the indices of the blocks along the diagonal
        DiagonalVector _diagonal;
    };
  
  } //end namespace
  
  #endif
  