text: // g2o - General Graph Optimization
  // Copyright (C) 2011 R. Kuemmerle, G. Grisetti, W. Burgard
  // All rights reserved.
  //
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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 "../../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::axpy(A, srcVec, srcOffset, destVec, destOffset);
  				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
  