text: // This file is part of Eigen, a lightweight C++ template library
  // for linear algebra.
  //
  // Copyright (C) 2008-2009 Gael Guennebaud <gael.guennebaud@inria.fr>
  //
  // This Source Code Form is subject to the terms of the Mozilla
  // Public License v. 2.0. If a copy of the MPL was not distributed
  // with this file, You can obtain one at http://mozilla.org/MPL/2.0/.
  
  #ifndef EIGEN_SPARSE_BLOCK_H
  #define EIGEN_SPARSE_BLOCK_H
  
  namespace Eigen { 
  
  template<typename XprType, int BlockRows, int BlockCols>
  class BlockImpl<XprType,BlockRows,BlockCols,true,Sparse>
    : public SparseMatrixBase<Block<XprType,BlockRows,BlockCols,true> >
  {
  public:
      typedef Block<XprType, BlockRows, BlockCols, true> BlockType;
      enum { IsRowMajor = internal::traits<BlockType>::IsRowMajor };
  protected:
    typedef typename internal::remove_all<typename XprType::Nested>::type _MatrixTypeNested;
      enum { OuterSize = IsRowMajor ? BlockRows : BlockCols };
  public:
      EIGEN_SPARSE_PUBLIC_INTERFACE(BlockType)
      
      class InnerIterator: public XprType::InnerIterator
      {
          typedef typename BlockImpl::Index Index;
        public:
          inline InnerIterator(const Block<XprType, BlockRows, BlockCols, true>& xpr, Index outer)
            : XprType::InnerIterator(xpr.m_matrix, xpr.m_outerStart + outer), m_outer(outer)
          {}
          inline Index row() const { return IsRowMajor ? m_outer : this->index(); }
          inline Index col() const { return IsRowMajor ? this->index() : m_outer; }
        protected:
           Index m_outer;
      };
      class ReverseInnerIterator: public XprType::ReverseInnerIterator
      {
          typedef typename BlockImpl::Index Index;
        public:
          inline ReverseInnerIterator(const BlockType& xpr, Index outer)
            : XprType::ReverseInnerIterator(xpr.m_matrix, xpr.m_outerStart + outer), m_outer(outer)
          {}
          inline Index row() const { return IsRowMajor ? m_outer : this->index(); }
          inline Index col() const { return IsRowMajor ? this->index() : m_outer; }
        protected:
          Index m_outer;
      };
  
      inline BlockImpl(const XprType& xpr, int i)
        : m_matrix(xpr), m_outerStart(i), m_outerSize(OuterSize)
      {}
  
      inline BlockImpl(const XprType& xpr, int startRow, int startCol, int blockRows, int blockCols)
        : m_matrix(xpr), m_outerStart(IsRowMajor ? startRow : startCol), m_outerSize(IsRowMajor ? blockRows : blockCols)
      {}
      
      inline const Scalar coeff(int row, int col) const
      {
        return m_matrix.coeff(row + IsRowMajor ? m_outerStart : 0, col +IsRowMajor ? 0 :  m_outerStart);
      }
      
      inline const Scalar coeff(int index) const
      {
        return m_matrix.coeff(IsRowMajor ? m_outerStart : index, IsRowMajor ? index :  m_outerStart);
      }
  
      EIGEN_STRONG_INLINE Index rows() const { return IsRowMajor ? m_outerSize.value() : m_matrix.rows(); }
      EIGEN_STRONG_INLINE Index cols() const { return IsRowMajor ? m_matrix.cols() : m_outerSize.value(); }
  
    protected:
  
      typename XprType::Nested m_matrix;
      Index m_outerStart;
      const internal::variable_if_dynamic<Index, OuterSize> m_outerSize;
  
      EIGEN_INHERIT_ASSIGNMENT_OPERATORS(BlockImpl)
    private:
      Index nonZeros() const;
  };
  
  
  /***************************************************************************
  * specialisation for SparseMatrix
  ***************************************************************************/
  
  template<typename _Scalar, int _Options, typename _Index, int BlockRows, int BlockCols>
  class BlockImpl<SparseMatrix<_Scalar, _Options, _Index>,BlockRows,BlockCols,true,Sparse>
    : public SparseMatrixBase<Block<SparseMatrix<_Scalar, _Options, _Index>,BlockRows,BlockCols,true> >
  {
      typedef SparseMatrix<_Scalar, _Options, _Index> SparseMatrixType;
      typedef typename internal::remove_all<typename SparseMatrixType::Nested>::type _MatrixTypeNested;
      typedef Block<const SparseMatrixType, BlockRows, BlockCols, true> ConstBlockType;
  public:
    typedef Block<SparseMatrixType, BlockRows, BlockCols, true> BlockType;
      enum { IsRowMajor = internal::traits<BlockType>::IsRowMajor };
      EIGEN_SPARSE_PUBLIC_INTERFACE(BlockType)
  protected:
      enum { OuterSize = IsRowMajor ? BlockRows : BlockCols };
  public:
      
      class InnerIterator: public SparseMatrixType::InnerIterator
      {
        public:
          inline InnerIterator(const BlockType& xpr, Index outer)
            : SparseMatrixType::InnerIterator(xpr.m_matrix, xpr.m_outerStart + outer), m_outer(outer)
          {}
          inline Index row() const { return IsRowMajor ? m_outer : this->index(); }
          inline Index col() const { return IsRowMajor ? this->index() : m_outer; }
        protected:
          Index m_outer;
      };
      class ReverseInnerIterator: public SparseMatrixType::ReverseInnerIterator
      {
        public:
          inline ReverseInnerIterator(const BlockType& xpr, Index outer)
            : SparseMatrixType::ReverseInnerIterator(xpr.m_matrix, xpr.m_outerStart + outer), m_outer(outer)
          {}
          inline Index row() const { return IsRowMajor ? m_outer : this->index(); }
          inline Index col() const { return IsRowMajor ? this->index() : m_outer; }
        protected:
          Index m_outer;
      };
  
      inline BlockImpl(const SparseMatrixType& xpr, int i)
        : m_matrix(xpr), m_outerStart(i), m_outerSize(OuterSize)
      {}
  
      inline BlockImpl(const SparseMatrixType& xpr, int startRow, int startCol, int blockRows, int blockCols)
        : m_matrix(xpr), m_outerStart(IsRowMajor ? startRow : startCol), m_outerSize(IsRowMajor ? blockRows : blockCols)
      {}
  
      template<typename OtherDerived>
      inline BlockType& operator=(const SparseMatrixBase<OtherDerived>& other)
      {
        typedef typename internal::remove_all<typename SparseMatrixType::Nested>::type _NestedMatrixType;
        _NestedMatrixType& matrix = const_cast<_NestedMatrixType&>(m_matrix);;
        // This assignement is slow if this vector set is not empty
        // and/or it is not at the end of the nonzeros of the underlying matrix.
  
        // 1 - eval to a temporary to avoid transposition and/or aliasing issues
        SparseMatrix<Scalar, IsRowMajor ? RowMajor : ColMajor, Index> tmp(other);
  
        // 2 - let's check whether there is enough allocated memory
        Index nnz           = tmp.nonZeros();
        Index start         = m_outerStart==0 ? 0 : matrix.outerIndexPtr()[m_outerStart]; // starting position of the current block
        Index end           = m_matrix.outerIndexPtr()[m_outerStart+m_outerSize.value()]; // ending posiiton of the current block
        Index block_size    = end - start;                                                // available room in the current block
        Index tail_size     = m_matrix.outerIndexPtr()[m_matrix.outerSize()] - end;
        
        Index free_size     = m_matrix.isCompressed()
                            ? Index(matrix.data().allocatedSize()) + block_size
                            : block_size;
  
        if(nnz>free_size) 
        {
          // realloc manually to reduce copies
          typename SparseMatrixType::Storage newdata(m_matrix.data().allocatedSize() - block_size + nnz);
  
          std::memcpy(newdata.valuePtr(), m_matrix.data().valuePtr(), start*sizeof(Scalar));
          std::memcpy(newdata.indexPtr(), m_matrix.data().indexPtr(), start*sizeof(Index));
  
          std::memcpy(newdata.valuePtr() + start, tmp.data().valuePtr(), nnz*sizeof(Scalar));
          std::memcpy(newdata.indexPtr() + start, tmp.data().indexPtr(), nnz*sizeof(Index));
  
          std::memcpy(newdata.valuePtr()+start+nnz, matrix.data().valuePtr()+end, tail_size*sizeof(Scalar));
          std::memcpy(newdata.indexPtr()+start+nnz, matrix.data().indexPtr()+end, tail_size*sizeof(Index));
          
          newdata.resize(m_matrix.outerIndexPtr()[m_matrix.outerSize()] - block_size + nnz);
  
          matrix.data().swap(newdata);
        }
        else
        {
          // no need to realloc, simply copy the tail at its respective position and insert tmp
          matrix.data().resize(start + nnz + tail_size);
  
          std::memmove(matrix.data().valuePtr()+start+nnz, matrix.data().valuePtr()+end, tail_size*sizeof(Scalar));
          std::memmove(matrix.data().indexPtr()+start+nnz, matrix.data().indexPtr()+end, tail_size*sizeof(Index));
  
          std::memcpy(matrix.data().valuePtr()+start, tmp.data().valuePtr(), nnz*sizeof(Scalar));
          std::memcpy(matrix.data().indexPtr()+start, tmp.data().indexPtr(), nnz*sizeof(Index));
        }
        
        // update innerNonZeros
        if(!m_matrix.isCompressed())
          for(Index j=0; j<m_outerSize.value(); ++j)
            matrix.innerNonZeroPtr()[m_outerStart+j] = tmp.innerVector(j).nonZeros();
  
        // update outer index pointers
        Index p = start;
        for(Index k=0; k<m_outerSize.value(); ++k)
        {
          matrix.outerIndexPtr()[m_outerStart+k] = p;
          p += tmp.innerVector(k).nonZeros();
        }
        std::ptrdiff_t offset = nnz - block_size;
        for(Index k = m_outerStart + m_outerSize.value(); k<=matrix.outerSize(); ++k)
        {
          matrix.outerIndexPtr()[k] += offset;
        }
  
        return derived();
      }
  
      inline BlockType& operator=(const BlockType& other)
      {
        return operator=<BlockType>(other);
      }
  
      inline const Scalar* valuePtr() const
      { return m_matrix.valuePtr() + m_matrix.outerIndexPtr()[m_outerStart]; }
      inline Scalar* valuePtr()
      { return m_matrix.const_cast_derived().valuePtr() + m_matrix.outerIndexPtr()[m_outerStart]; }
  
      inline const Index* innerIndexPtr() const
      { return m_matrix.innerIndexPtr() + m_matrix.outerIndexPtr()[m_outerStart]; }
      inline Index* innerIndexPtr()
      { return m_matrix.const_cast_derived().innerIndexPtr() + m_matrix.outerIndexPtr()[m_outerStart]; }
  
      inline const Index* outerIndexPtr() const
      { return m_matrix.outerIndexPtr() + m_outerStart; }
      inline Index* outerIndexPtr()
      { return m_matrix.const_cast_derived().outerIndexPtr() + m_outerStart; }
  
      Index nonZeros() const
      {
        if(m_matrix.isCompressed())
          return  std::size_t(m_matrix.outerIndexPtr()[m_outerStart+m_outerSize.value()])
                - std::size_t(m_matrix.outerIndexPtr()[m_outerStart]);
        else if(m_outerSize.value()==0)
          return 0;
        else
          return Map<const Matrix<Index,OuterSize,1> >(m_matrix.innerNonZeroPtr()+m_outerStart, m_outerSize.value()).sum();
      }
      
      inline Scalar& coeffRef(int row, int col)
      {
        return m_matrix.const_cast_derived().coeffRef(row + (IsRowMajor ? m_outerStart : 0), col + (IsRowMajor ? 0 :  m_outerStart));
      }
      
      inline const Scalar coeff(int row, int col) const
      {
        return m_matrix.coeff(row + (IsRowMajor ? m_outerStart : 0), col + (IsRowMajor ? 0 :  m_outerStart));
      }
      
      inline const Scalar coeff(int index) const
      {
        return m_matrix.coeff(IsRowMajor ? m_outerStart : index, IsRowMajor ? index :  m_outerStart);
      }
  
      const Scalar& lastCoeff() const
      {
        EIGEN_STATIC_ASSERT_VECTOR_ONLY(BlockImpl);
        eigen_assert(nonZeros()>0);
        if(m_matrix.isCompressed())
          return m_matrix.valuePtr()[m_matrix.outerIndexPtr()[m_outerStart+1]-1];
        else
          return m_matrix.valuePtr()[m_matrix.outerIndexPtr()[m_outerStart]+m_matrix.innerNonZeroPtr()[m_outerStart]-1];
      }
  
      EIGEN_STRONG_INLINE Index rows() const { return IsRowMajor ? m_outerSize.value() : m_matrix.rows(); }
      EIGEN_STRONG_INLINE Index cols() const { return IsRowMajor ? m_matrix.cols() : m_outerSize.value(); }
  
    protected:
  
      typename SparseMatrixType::Nested m_matrix;
      Index m_outerStart;
      const internal::variable_if_dynamic<Index, OuterSize> m_outerSize;
  
  };
  
  
  template<typename _Scalar, int _Options, typename _Index, int BlockRows, int BlockCols>
  class BlockImpl<const SparseMatrix<_Scalar, _Options, _Index>,BlockRows,BlockCols,true,Sparse>
    : public SparseMatrixBase<Block<const SparseMatrix<_Scalar, _Options, _Index>,BlockRows,BlockCols,true> >
  {
      typedef SparseMatrix<_Scalar, _Options, _Index> SparseMatrixType;
      typedef typename internal::remove_all<typename SparseMatrixType::Nested>::type _MatrixTypeNested;
  public:
    typedef Block<const SparseMatrixType, BlockRows, BlockCols, true> BlockType;
      enum { IsRowMajor = internal::traits<BlockType>::IsRowMajor };
      EIGEN_SPARSE_PUBLIC_INTERFACE(BlockType)
  protected:
      enum { OuterSize = IsRowMajor ? BlockRows : BlockCols };
  public:
      
      class InnerIterator: public SparseMatrixType::InnerIterator
      {
        public:
          inline InnerIterator(const BlockType& xpr, Index outer)
            : SparseMatrixType::InnerIterator(xpr.m_matrix, xpr.m_outerStart + outer), m_outer(outer)
          {}
          inline Index row() const { return IsRowMajor ? m_outer : this->index(); }
          inline Index col() const { return IsRowMajor ? this->index() : m_outer; }
        protected:
          Index m_outer;
      };
      class ReverseInnerIterator: public SparseMatrixType::ReverseInnerIterator
      {
        public:
          inline ReverseInnerIterator(const BlockType& xpr, Index outer)
            : SparseMatrixType::ReverseInnerIterator(xpr.m_matrix, xpr.m_outerStart + outer), m_outer(outer)
          {}
          inline Index row() const { return IsRowMajor ? m_outer : this->index(); }
          inline Index col() const { return IsRowMajor ? this->index() : m_outer; }
        protected:
          Index m_outer;
      };
  
      inline BlockImpl(const SparseMatrixType& xpr, int i)
        : m_matrix(xpr), m_outerStart(i), m_outerSize(OuterSize)
      {}
  
      inline BlockImpl(const SparseMatrixType& xpr, int startRow, int startCol, int blockRows, int blockCols)
        : m_matrix(xpr), m_outerStart(IsRowMajor ? startRow : startCol), m_outerSize(IsRowMajor ? blockRows : blockCols)
      {}
  
      inline const Scalar* valuePtr() const
      { return m_matrix.valuePtr() + m_matrix.outerIndexPtr()[m_outerStart]; }
  
      inline const Index* innerIndexPtr() const
      { return m_matrix.innerIndexPtr() + m_matrix.outerIndexPtr()[m_outerStart]; }
  
      inline const Index* outerIndexPtr() const
      { return m_matrix.outerIndexPtr() + m_outerStart; }
  
      Index nonZeros() const
      {
        if(m_matrix.isCompressed())
          return  std::size_t(m_matrix.outerIndexPtr()[m_outerStart+m_outerSize.value()])
                - std::size_t(m_matrix.outerIndexPtr()[m_outerStart]);
        else if(m_outerSize.value()==0)
          return 0;
        else
          return Map<const Matrix<Index,OuterSize,1> >(m_matrix.innerNonZeroPtr()+m_outerStart, m_outerSize.value()).sum();
      }
      
      inline const Scalar coeff(int row, int col) const
      {
        return m_matrix.coeff(row + (IsRowMajor ? m_outerStart : 0), col + (IsRowMajor ? 0 :  m_outerStart));
      }
      
      inline const Scalar coeff(int index) const
      {
        return m_matrix.coeff(IsRowMajor ? m_outerStart : index, IsRowMajor ? index :  m_outerStart);
      }
  
      const Scalar& lastCoeff() const
      {
        EIGEN_STATIC_ASSERT_VECTOR_ONLY(BlockImpl);
        eigen_assert(nonZeros()>0);
        if(m_matrix.isCompressed())
          return m_matrix.valuePtr()[m_matrix.outerIndexPtr()[m_outerStart+1]-1];
        else
          return m_matrix.valuePtr()[m_matrix.outerIndexPtr()[m_outerStart]+m_matrix.innerNonZeroPtr()[m_outerStart]-1];
      }
  
      EIGEN_STRONG_INLINE Index rows() const { return IsRowMajor ? m_outerSize.value() : m_matrix.rows(); }
      EIGEN_STRONG_INLINE Index cols() const { return IsRowMajor ? m_matrix.cols() : m_outerSize.value(); }
  
    protected:
  
      EIGEN_INHERIT_ASSIGNMENT_OPERATORS(BlockImpl)
  
      typename SparseMatrixType::Nested m_matrix;
      Index m_outerStart;
      const internal::variable_if_dynamic<Index, OuterSize> m_outerSize;
  };
  
  //----------
  
  /** \returns the \a outer -th column (resp. row) of the matrix \c *this if \c *this
    * is col-major (resp. row-major).
    */
  template<typename Derived>
  typename SparseMatrixBase<Derived>::InnerVectorReturnType SparseMatrixBase<Derived>::innerVector(Index outer)
  { return InnerVectorReturnType(derived(), outer); }
  
  /** \returns the \a outer -th column (resp. row) of the matrix \c *this if \c *this
    * is col-major (resp. row-major). Read-only.
    */
  template<typename Derived>
  const typename SparseMatrixBase<Derived>::ConstInnerVectorReturnType SparseMatrixBase<Derived>::innerVector(Index outer) const
  { return ConstInnerVectorReturnType(derived(), outer); }
  
  /** \returns the \a outer -th column (resp. row) of the matrix \c *this if \c *this
    * is col-major (resp. row-major).
    */
  template<typename Derived>
  typename SparseMatrixBase<Derived>::InnerVectorsReturnType
  SparseMatrixBase<Derived>::innerVectors(Index outerStart, Index outerSize)
  {
    return Block<Derived,Dynamic,Dynamic,true>(derived(),
                                               IsRowMajor ? outerStart : 0, IsRowMajor ? 0 : outerStart,
                                               IsRowMajor ? outerSize : rows(), IsRowMajor ? cols() : outerSize);
    
  }
  
  /** \returns the \a outer -th column (resp. row) of the matrix \c *this if \c *this
    * is col-major (resp. row-major). Read-only.
    */
  template<typename Derived>
  const typename SparseMatrixBase<Derived>::ConstInnerVectorsReturnType
  SparseMatrixBase<Derived>::innerVectors(Index outerStart, Index outerSize) const
  {
    return Block<const Derived,Dynamic,Dynamic,true>(derived(),
                                                    IsRowMajor ? outerStart : 0, IsRowMajor ? 0 : outerStart,
                                                    IsRowMajor ? outerSize : rows(), IsRowMajor ? cols() : outerSize);
    
  }
  
  namespace internal {
    
  template< typename XprType, int BlockRows, int BlockCols, bool InnerPanel,
            bool OuterVector =  (BlockCols==1 && XprType::IsRowMajor) || (BlockRows==1 && !XprType::IsRowMajor)>
  class GenericSparseBlockInnerIteratorImpl;
  
  }
  
  /** Generic implementation of sparse Block expression.
    * Real-only. 
    */
  template<typename XprType, int BlockRows, int BlockCols, bool InnerPanel>
  class BlockImpl<XprType,BlockRows,BlockCols,InnerPanel,Sparse>
    : public SparseMatrixBase<Block<XprType,BlockRows,BlockCols,InnerPanel> >, internal::no_assignment_operator
  {
      typedef typename internal::remove_all<typename XprType::Nested>::type _MatrixTypeNested;
    public:
      typedef Block<XprType, BlockRows, BlockCols, InnerPanel> BlockType;
      enum { IsRowMajor = internal::traits<BlockType>::IsRowMajor };
      EIGEN_SPARSE_PUBLIC_INTERFACE(BlockType)
  
      /** Column or Row constructor
        */
      inline BlockImpl(const XprType& xpr, int i)
        : m_matrix(xpr),
          m_startRow( (BlockRows==1) && (BlockCols==XprType::ColsAtCompileTime) ? i : 0),
          m_startCol( (BlockRows==XprType::RowsAtCompileTime) && (BlockCols==1) ? i : 0),
          m_blockRows(BlockRows==1 ? 1 : xpr.rows()),
          m_blockCols(BlockCols==1 ? 1 : xpr.cols())
      {}
  
      /** Dynamic-size constructor
        */
      inline BlockImpl(const XprType& xpr, int startRow, int startCol, int blockRows, int blockCols)
        : m_matrix(xpr), m_startRow(startRow), m_startCol(startCol), m_blockRows(blockRows), m_blockCols(blockCols)
      {}
  
      inline int rows() const { return m_blockRows.value(); }
      inline int cols() const { return m_blockCols.value(); }
  
      inline Scalar& coeffRef(int row, int col)
      {
        return m_matrix.const_cast_derived()
                 .coeffRef(row + m_startRow.value(), col + m_startCol.value());
      }
  
      inline const Scalar coeff(int row, int col) const
      {
        return m_matrix.coeff(row + m_startRow.value(), col + m_startCol.value());
      }
  
      inline Scalar& coeffRef(int index)
      {
        return m_matrix.const_cast_derived()
               .coeffRef(m_startRow.value() + (RowsAtCompileTime == 1 ? 0 : index),
                         m_startCol.value() + (RowsAtCompileTime == 1 ? index : 0));
      }
  
      inline const Scalar coeff(int index) const
      {
        return m_matrix
               .coeff(m_startRow.value() + (RowsAtCompileTime == 1 ? 0 : index),
                      m_startCol.value() + (RowsAtCompileTime == 1 ? index : 0));
      }
      
      inline const _MatrixTypeNested& nestedExpression() const { return m_matrix; }
      
      typedef internal::GenericSparseBlockInnerIteratorImpl<XprType,BlockRows,BlockCols,InnerPanel> InnerIterator;
      
      class ReverseInnerIterator : public _MatrixTypeNested::ReverseInnerIterator
      {
        typedef typename _MatrixTypeNested::ReverseInnerIterator Base;
        const BlockType& m_block;
        Index m_begin;
      public:
  
        EIGEN_STRONG_INLINE ReverseInnerIterator(const BlockType& block, Index outer)
          : Base(block.derived().nestedExpression(), outer + (IsRowMajor ? block.m_startRow.value() : block.m_startCol.value())),
            m_block(block),
            m_begin(IsRowMajor ? block.m_startCol.value() : block.m_startRow.value())
        {
          while( (Base::operator bool()) && (Base::index() >= (IsRowMajor ? m_block.m_startCol.value()+block.m_blockCols.value() : m_block.m_startRow.value()+block.m_blockRows.value())) )
            Base::operator--();
        }
  
        inline Index index()  const { return Base::index() - (IsRowMajor ? m_block.m_startCol.value() : m_block.m_startRow.value()); }
        inline Index outer()  const { return Base::outer() - (IsRowMajor ? m_block.m_startRow.value() : m_block.m_startCol.value()); }
        inline Index row()    const { return Base::row()   - m_block.m_startRow.value(); }
        inline Index col()    const { return Base::col()   - m_block.m_startCol.value(); }
        
        inline operator bool() const { return Base::operator bool() && Base::index() >= m_begin; }
      };
    protected:
      friend class internal::GenericSparseBlockInnerIteratorImpl<XprType,BlockRows,BlockCols,InnerPanel>;
      friend class ReverseInnerIterator;
      
      EIGEN_INHERIT_ASSIGNMENT_OPERATORS(BlockImpl)
  
      typename XprType::Nested m_matrix;
      const internal::variable_if_dynamic<Index, XprType::RowsAtCompileTime == 1 ? 0 : Dynamic> m_startRow;
      const internal::variable_if_dynamic<Index, XprType::ColsAtCompileTime == 1 ? 0 : Dynamic> m_startCol;
      const internal::variable_if_dynamic<Index, RowsAtCompileTime> m_blockRows;
      const internal::variable_if_dynamic<Index, ColsAtCompileTime> m_blockCols;
    private:
      Index nonZeros() const;
  };
  
  namespace internal {
    template<typename XprType, int BlockRows, int BlockCols, bool InnerPanel>
    class GenericSparseBlockInnerIteratorImpl<XprType,BlockRows,BlockCols,InnerPanel,false> : public internal::remove_all<typename XprType::Nested>::type::InnerIterator
    {
    public:
      typedef Block<XprType, BlockRows, BlockCols, InnerPanel> BlockType;
      enum {
        IsRowMajor = BlockType::IsRowMajor
      };
      typedef typename BlockType::Index Index;
    protected:
      typedef typename internal::remove_all<typename XprType::Nested>::type _MatrixTypeNested;
      typedef typename _MatrixTypeNested::InnerIterator Base;
      const BlockType& m_block;
      Index m_end;
    public:
  
      EIGEN_STRONG_INLINE GenericSparseBlockInnerIteratorImpl(const BlockType& block, Index outer)
        : Base(block.derived().nestedExpression(), outer + (IsRowMajor ? block.m_startRow.value() : block.m_startCol.value())),
          m_block(block),
          m_end(IsRowMajor ? block.m_startCol.value()+block.m_blockCols.value() : block.m_startRow.value()+block.m_blockRows.value())
      {
        while( (Base::operator bool()) && (Base::index() < (IsRowMajor ? m_block.m_startCol.value() : m_block.m_startRow.value())) )
          Base::operator++();
      }
      
      inline Index index()  const { return Base::index() - (IsRowMajor ? m_block.m_startCol.value() : m_block.m_startRow.value()); }
      inline Index outer()  const { return Base::outer() - (IsRowMajor ? m_block.m_startRow.value() : m_block.m_startCol.value()); }
      inline Index row()    const { return Base::row()   - m_block.m_startRow.value(); }
      inline Index col()    const { return Base::col()   - m_block.m_startCol.value(); }
      
      inline operator bool() const { return Base::operator bool() && Base::index() < m_end; }
    };
    
    // Row vector of a column-major sparse matrix or column of a row-major one.
    template<typename XprType, int BlockRows, int BlockCols, bool InnerPanel>
    class GenericSparseBlockInnerIteratorImpl<XprType,BlockRows,BlockCols,InnerPanel,true>
    {
    public:
      typedef Block<XprType, BlockRows, BlockCols, InnerPanel> BlockType;
      enum {
        IsRowMajor = BlockType::IsRowMajor
      };
      typedef typename BlockType::Index Index;
      typedef typename BlockType::Scalar Scalar;
    protected:
      typedef typename internal::remove_all<typename XprType::Nested>::type _MatrixTypeNested;
      const BlockType& m_block;
      Index m_outerPos;
      Index m_innerIndex;
      Scalar m_value;
      Index m_end;
    public:
  
      EIGEN_STRONG_INLINE GenericSparseBlockInnerIteratorImpl(const BlockType& block, Index outer = 0)
        : 
          m_block(block),
          m_outerPos( (IsRowMajor ? block.m_startCol.value() : block.m_startRow.value()) - 1), // -1 so that operator++ finds the first non-zero entry
          m_innerIndex(IsRowMajor ? block.m_startRow.value() : block.m_startCol.value()),
          m_end(IsRowMajor ? block.m_startCol.value()+block.m_blockCols.value() : block.m_startRow.value()+block.m_blockRows.value())
      {
        EIGEN_UNUSED_VARIABLE(outer);
        eigen_assert(outer==0);
        
        ++(*this);
      }
      
      inline Index index()  const { return m_outerPos - (IsRowMajor ? m_block.m_startCol.value() : m_block.m_startRow.value()); }
      inline Index outer()  const { return 0; }
      inline Index row()    const { return IsRowMajor ? 0 : index(); }
      inline Index col()    const { return IsRowMajor ? index() : 0; }
      
      inline Scalar value() const { return m_value; }
      
      inline GenericSparseBlockInnerIteratorImpl& operator++()
      {
        // search next non-zero entry
        while(m_outerPos<m_end)
        {
          m_outerPos++;
          typename XprType::InnerIterator it(m_block.m_matrix, m_outerPos);
          // search for the key m_innerIndex in the current outer-vector
          while(it && it.index() < m_innerIndex) ++it;
          if(it && it.index()==m_innerIndex)
          {
            m_value = it.value();
            break;
          }
        }
        return *this;
      }
      
      inline operator bool() const { return m_outerPos < m_end; }
    };
    
  } // end namespace internal
  
  
  } // end namespace Eigen
  
  #endif // EIGEN_SPARSE_BLOCK_H
  