sparse_block_matrix.hpp

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// 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
// 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.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
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// TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
// PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
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namespace g2o {
  using namespace Eigen;

  namespace {
    struct TripletEntry
    {
      int r, c;
      double x;
      TripletEntry(int r_, int c_, double x_) : r(r_), c(c_), x(x_) {}
    };
    struct TripletColSort
    {
      bool operator()(const TripletEntry& e1, const TripletEntry& e2) const
      {
        return e1.c < e2.c || (e1.c == e2.c && e1.r < e2.r);
      }
    };
    template<class T1, class T2, class Pred = std::less<T1> >
    struct CmpPairFirst {
      bool operator()(const std::pair<T1,T2>& left, const std::pair<T1,T2>& right) {
        return Pred()(left.first, right.first);
      }
    };
  }

  template <class MatrixType>
  SparseBlockMatrix<MatrixType>::SparseBlockMatrix( const int * rbi, const int* cbi, int rb, int cb, bool hasStorage):
    _rowBlockIndices(rbi,rbi+rb),
    _colBlockIndices(cbi,cbi+cb),
    _blockCols(cb), _hasStorage(hasStorage) 
  {
  }

  template <class MatrixType>
  SparseBlockMatrix<MatrixType>::SparseBlockMatrix( ):
    _blockCols(0), _hasStorage(true) 
  {
  }

  template <class MatrixType>
  void SparseBlockMatrix<MatrixType>::clear(bool dealloc) {
#   ifdef G2O_OPENMP
#   pragma omp parallel for default (shared) if (_blockCols.size() > 100)
#   endif
    for (int i=0; i < static_cast<int>(_blockCols.size()); ++i) {
      for (typename SparseBlockMatrix<MatrixType>::IntBlockMap::const_iterator it=_blockCols[i].begin(); it!=_blockCols[i].end(); ++it){
        typename SparseBlockMatrix<MatrixType>::SparseMatrixBlock* b=it->second;
        if (_hasStorage && dealloc)
          delete b;
        else
          b->setZero();
      }
      if (_hasStorage && dealloc)
        _blockCols[i].clear();
    }
  }

  template <class MatrixType>
  SparseBlockMatrix<MatrixType>::~SparseBlockMatrix(){
    if (_hasStorage)
      clear(true);
  }

  template <class MatrixType>
  typename SparseBlockMatrix<MatrixType>::SparseMatrixBlock* SparseBlockMatrix<MatrixType>::block(int r, int c, bool alloc) {
    typename SparseBlockMatrix<MatrixType>::IntBlockMap::iterator it =_blockCols[c].find(r);
    typename SparseBlockMatrix<MatrixType>::SparseMatrixBlock* _block=0;
    if (it==_blockCols[c].end()){
      if (!_hasStorage && ! alloc )
        return 0;
      else {
        int rb=rowsOfBlock(r);
        int cb=colsOfBlock(c);
        _block=new typename SparseBlockMatrix<MatrixType>::SparseMatrixBlock(rb,cb);
        _block->setZero();
        std::pair < typename SparseBlockMatrix<MatrixType>::IntBlockMap::iterator, bool> result
          =_blockCols[c].insert(std::make_pair(r,_block)); (void) result;
        assert (result.second);
      }
    } else {
      _block=it->second;
    }
    return _block;
  }

  template <class MatrixType>
  const typename SparseBlockMatrix<MatrixType>::SparseMatrixBlock* SparseBlockMatrix<MatrixType>::block(int r, int c) const {
    typename SparseBlockMatrix<MatrixType>::IntBlockMap::const_iterator it =_blockCols[c].find(r);
    if (it==_blockCols[c].end())
  return 0;
    return it->second;
  }


  template <class MatrixType>
  SparseBlockMatrix<MatrixType>* SparseBlockMatrix<MatrixType>::clone() const {
    SparseBlockMatrix* ret= new SparseBlockMatrix(&_rowBlockIndices[0], &_colBlockIndices[0], _rowBlockIndices.size(), _colBlockIndices.size());
    for (size_t i=0; i<_blockCols.size(); ++i){
      for (typename SparseBlockMatrix<MatrixType>::IntBlockMap::const_iterator it=_blockCols[i].begin(); it!=_blockCols[i].end(); ++it){
        typename SparseBlockMatrix<MatrixType>::SparseMatrixBlock* b=new typename SparseBlockMatrix<MatrixType>::SparseMatrixBlock(*it->second);
        ret->_blockCols[i].insert(std::make_pair(it->first, b));
      }
    }
    ret->_hasStorage=true;
    return ret;
  }


  template <class MatrixType>
  template <class MatrixTransposedType>
  bool SparseBlockMatrix<MatrixType>::transpose(SparseBlockMatrix<MatrixTransposedType>*& dest) const {
    if (! dest){
      dest=new SparseBlockMatrix<MatrixTransposedType>(&_colBlockIndices[0], &_rowBlockIndices[0], _colBlockIndices.size(), _rowBlockIndices.size());
    } else {
      if (! dest->_hasStorage)
        return false;
      if(_rowBlockIndices.size()!=dest->_colBlockIndices.size())
        return false;
      if (_colBlockIndices.size()!=dest->_rowBlockIndices.size())
        return  false;
      for (size_t i=0; i<_rowBlockIndices.size(); ++i){
        if(_rowBlockIndices[i]!=dest->_colBlockIndices[i])
          return false;
      }
      for (size_t i=0; i<_colBlockIndices.size(); ++i){
        if(_colBlockIndices[i]!=dest->_rowBlockIndices[i])
          return false;
      }
    }

    for (size_t i=0; i<_blockCols.size(); ++i){
      for (typename SparseBlockMatrix<MatrixType>::IntBlockMap::const_iterator it=_blockCols[i].begin(); it!=_blockCols[i].end(); ++it){
        typename SparseBlockMatrix<MatrixType>::SparseMatrixBlock* s=it->second;
        typename SparseBlockMatrix<MatrixTransposedType>::SparseMatrixBlock* d=dest->block(i,it->first,true);
        *d = s->transpose();
      }
    }
    return true;
  }

  template <class MatrixType>
  bool SparseBlockMatrix<MatrixType>::add(SparseBlockMatrix*& dest) const {
    if (! dest){
      dest=new SparseBlockMatrix(&_rowBlockIndices[0], &_colBlockIndices[0], _rowBlockIndices.size(), _colBlockIndices.size());
    } else {
      if (! dest->_hasStorage)
        return false;
      if(_rowBlockIndices.size()!=dest->_rowBlockIndices.size())
        return false;
      if (_colBlockIndices.size()!=dest->_colBlockIndices.size())
        return  false;
      for (size_t i=0; i<_rowBlockIndices.size(); ++i){
        if(_rowBlockIndices[i]!=dest->_rowBlockIndices[i])
          return false;
      }
      for (size_t i=0; i<_colBlockIndices.size(); ++i){
        if(_colBlockIndices[i]!=dest->_colBlockIndices[i])
          return false;
      }
    }
    for (size_t i=0; i<_blockCols.size(); ++i){
      for (typename SparseBlockMatrix<MatrixType>::IntBlockMap::const_iterator it=_blockCols[i].begin(); it!=_blockCols[i].end(); ++it){
        typename SparseBlockMatrix<MatrixType>::SparseMatrixBlock* s=it->second;
        typename SparseBlockMatrix<MatrixType>::SparseMatrixBlock* d=dest->block(it->first,i,true);
        (*d)+=*s;
      }
    }
    return true;
  }

  template <class MatrixType>
  template < class MatrixResultType, class MatrixFactorType >
  bool SparseBlockMatrix<MatrixType>::multiply(SparseBlockMatrix<MatrixResultType>*& dest, const SparseBlockMatrix<MatrixFactorType> * M) const {
    // sanity check
    if (_colBlockIndices.size()!=M->_rowBlockIndices.size())
      return false;
    for (size_t i=0; i<_colBlockIndices.size(); ++i){
      if (_colBlockIndices[i]!=M->_rowBlockIndices[i])
        return false;
    }
    if (! dest) {
      dest=new SparseBlockMatrix<MatrixResultType>(&_rowBlockIndices[0],&(M->_colBlockIndices[0]), _rowBlockIndices.size(), M->_colBlockIndices.size() );
    }
    if (! dest->_hasStorage)
      return false;
    for (size_t i=0; i<M->_blockCols.size(); ++i){
      for (typename SparseBlockMatrix<MatrixFactorType>::IntBlockMap::const_iterator it=M->_blockCols[i].begin(); it!=M->_blockCols[i].end(); ++it){
        // look for a non-zero block in a row of column it
        int colM=i;
        const typename SparseBlockMatrix<MatrixFactorType>::SparseMatrixBlock *b=it->second;
        typename SparseBlockMatrix<MatrixType>::IntBlockMap::const_iterator rbt=_blockCols[it->first].begin();
        while(rbt!=_blockCols[it->first].end()){
          //int colA=it->first;
          int rowA=rbt->first;
          typename SparseBlockMatrix<MatrixType>::SparseMatrixBlock *a=rbt->second;
          typename SparseBlockMatrix<MatrixResultType>::SparseMatrixBlock *c=dest->block(rowA,colM,true);
          assert (c->rows()==a->rows());
          assert (c->cols()==b->cols());
          ++rbt;
          (*c)+=(*a)*(*b);
        }
      }
    }
    return false;
  }

  template <class MatrixType>
  void SparseBlockMatrix<MatrixType>::multiply(double*& dest, const double* src) const {
    if (! dest){
      dest=new double [_rowBlockIndices[_rowBlockIndices.size()-1] ];
      memset(dest,0, _rowBlockIndices[_rowBlockIndices.size()-1]*sizeof(double));
    }

    // map the memory by Eigen
    Eigen::Map<VectorXd> destVec(dest, rows());
    const Eigen::Map<const VectorXd> srcVec(src, cols());

    for (size_t i=0; i<_blockCols.size(); ++i){
      int srcOffset = i ? _colBlockIndices[i-1] : 0;

      for (typename SparseBlockMatrix<MatrixType>::IntBlockMap::const_iterator it=_blockCols[i].begin(); it!=_blockCols[i].end(); ++it){
        const typename SparseBlockMatrix<MatrixType>::SparseMatrixBlock* a=it->second;
        int destOffset = it->first ? _rowBlockIndices[it->first - 1] : 0;
        // destVec += *a * srcVec (according to the sub-vector parts)
        internal::axpy(*a, srcVec, srcOffset, destVec, destOffset);
      }
    }
  }

  template <class MatrixType>
  void SparseBlockMatrix<MatrixType>::multiplySymmetricUpperTriangle(double*& dest, const double* src) const
  {
    if (! dest){
      dest=new double [_rowBlockIndices[_rowBlockIndices.size()-1] ];
      memset(dest,0, _rowBlockIndices[_rowBlockIndices.size()-1]*sizeof(double));
    }

    // map the memory by Eigen
    Eigen::Map<VectorXd> destVec(dest, rows());
    const Eigen::Map<const VectorXd> srcVec(src, cols());

    for (size_t i=0; i<_blockCols.size(); ++i){
      int srcOffset = colBaseOfBlock(i);
      for (typename SparseBlockMatrix<MatrixType>::IntBlockMap::const_iterator it=_blockCols[i].begin(); it!=_blockCols[i].end(); ++it){
        const typename SparseBlockMatrix<MatrixType>::SparseMatrixBlock* a=it->second;
        int destOffset = rowBaseOfBlock(it->first);
        if (destOffset > srcOffset) // only upper triangle
          break;
        // destVec += *a * srcVec (according to the sub-vector parts)
        internal::axpy(*a, srcVec, srcOffset, destVec, destOffset);
        if (destOffset < srcOffset)
          internal::atxpy(*a, srcVec, destOffset, destVec, srcOffset);
      }
    }
  }

  template <class MatrixType>
  void SparseBlockMatrix<MatrixType>::rightMultiply(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<VectorXd> destVec(dest, destSize);
    Eigen::Map<const 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>(_blockCols.size()); ++i){
      int destOffset = colBaseOfBlock(i);
      for (typename SparseBlockMatrix<MatrixType>::IntBlockMap::const_iterator it=_blockCols[i].begin(); 
          it!=_blockCols[i].end(); 
          ++it){
        const typename SparseBlockMatrix<MatrixType>::SparseMatrixBlock* a=it->second;
        int srcOffset = rowBaseOfBlock(it->first);
        // destVec += *a.transpose() * srcVec (according to the sub-vector parts)
        internal::atxpy(*a, srcVec, srcOffset, destVec, destOffset);
      }
    }
    
  }

  template <class MatrixType>
  void SparseBlockMatrix<MatrixType>::scale(double a_) {
    for (size_t i=0; i<_blockCols.size(); ++i){
      for (typename SparseBlockMatrix<MatrixType>::IntBlockMap::const_iterator it=_blockCols[i].begin(); it!=_blockCols[i].end(); ++it){
        typename SparseBlockMatrix<MatrixType>::SparseMatrixBlock* a=it->second;
        *a *= a_;
      }
    }
  }

  template <class MatrixType>
  SparseBlockMatrix<MatrixType>*  SparseBlockMatrix<MatrixType>::slice(int rmin, int rmax, int cmin, int cmax, bool alloc) const {
    int m=rmax-rmin;
    int n=cmax-cmin;
    int rowIdx [m];
    rowIdx[0] = rowsOfBlock(rmin);
    for (int i=1; i<m; ++i){
      rowIdx[i]=rowIdx[i-1]+rowsOfBlock(rmin+i);
    }

    int colIdx [n];
    colIdx[0] = colsOfBlock(cmin);
    for (int i=1; i<n; ++i){
      colIdx[i]=colIdx[i-1]+colsOfBlock(cmin+i);
    }
    typename SparseBlockMatrix<MatrixType>::SparseBlockMatrix* s=new SparseBlockMatrix(rowIdx, colIdx, m, n, true);
    for (int i=0; i<n; ++i){
      int mc=cmin+i;
      for (typename SparseBlockMatrix<MatrixType>::IntBlockMap::const_iterator it=_blockCols[mc].begin(); it!=_blockCols[mc].end(); ++it){
        if (it->first >= rmin && it->first < rmax){
          typename SparseBlockMatrix<MatrixType>::SparseMatrixBlock* b = alloc ? new typename SparseBlockMatrix<MatrixType>::SparseMatrixBlock (* (it->second) ) : it->second;
          s->_blockCols[i].insert(std::make_pair(it->first-rmin, b));
        }
      }
    }
    s->_hasStorage=alloc;
    return s;
  }

  template <class MatrixType>
  size_t SparseBlockMatrix<MatrixType>::nonZeroBlocks() const {
    size_t count=0;
    for (size_t i=0; i<_blockCols.size(); ++i)
      count+=_blockCols[i].size();
    return count;
  }

  template <class MatrixType>
  size_t SparseBlockMatrix<MatrixType>::nonZeros() const{
    if (MatrixType::SizeAtCompileTime != Eigen::Dynamic) {
      size_t nnz = nonZeroBlocks() * MatrixType::SizeAtCompileTime;
      return nnz;
    } else {
      size_t count=0;
      for (size_t i=0; i<_blockCols.size(); ++i){
        for (typename SparseBlockMatrix<MatrixType>::IntBlockMap::const_iterator it=_blockCols[i].begin(); it!=_blockCols[i].end(); ++it){
          const typename SparseBlockMatrix<MatrixType>::SparseMatrixBlock* a=it->second;
          count += a->cols()*a->rows();
        }
      }
      return count;
    }
  }

  template <class MatrixType>
  std::ostream& operator << (std::ostream& os, const SparseBlockMatrix<MatrixType>& m){
    os << "RBI: " << m.rowBlockIndices().size();
    for (size_t i=0; i<m.rowBlockIndices().size(); ++i)
      os << " " << m.rowBlockIndices()[i];
    os << std::endl;
    os << "CBI: " << m.colBlockIndices().size();
    for (size_t i=0; i<m.colBlockIndices().size(); ++i)
      os << " " << m.colBlockIndices()[i];
    os << std::endl;

    for (size_t i=0; i<m.blockCols().size(); ++i){
      for (typename SparseBlockMatrix<MatrixType>::IntBlockMap::const_iterator it=m.blockCols()[i].begin(); it!=m.blockCols()[i].end(); ++it){
        const typename SparseBlockMatrix<MatrixType>::SparseMatrixBlock* b=it->second;
        os << "BLOCK: " << it->first << " " << i << std::endl;
        os << *b << std::endl;
      }
    }
    return os;
  }

  template <class MatrixType>
  bool SparseBlockMatrix<MatrixType>::symmPermutation(SparseBlockMatrix<MatrixType>*& dest, const int* pinv, bool  upperTriangle) const{
    // compute the permuted version of the new row/column layout
    size_t n=_rowBlockIndices.size();
    // computed the block sizes
    int blockSizes[_rowBlockIndices.size()];
    blockSizes[0]=_rowBlockIndices[0];
    for (size_t i=1; i<n; ++i){
      blockSizes[i]=_rowBlockIndices[i]-_rowBlockIndices[i-1];
    }
    // permute them
    int pBlockIndices[_rowBlockIndices.size()];
    for (size_t i=0; i<n; ++i){
      pBlockIndices[pinv[i]]=blockSizes[i];
    }
    for (size_t i=1; i<n; ++i){
      pBlockIndices[i]+=pBlockIndices[i-1];
    }
    // allocate C, or check the structure;
    if (! dest){
      dest=new SparseBlockMatrix(pBlockIndices, pBlockIndices, n, n);
    } else {
      if (dest->_rowBlockIndices.size()!=n)
        return false;
      if (dest->_colBlockIndices.size()!=n)
        return false;
      for (size_t i=0; i<n; ++i){
        if (dest->_rowBlockIndices[i]!=pBlockIndices[i])
          return false;
        if (dest->_colBlockIndices[i]!=pBlockIndices[i])
          return false;
      }
      dest->clear();
    }
    // now ready to permute the columns
    for (size_t i=0; i<n; ++i){
      //cerr << PVAR(i) <<  " ";
      int pi=pinv[i];
      for (typename SparseBlockMatrix<MatrixType>::IntBlockMap::const_iterator it=_blockCols[i].begin(); 
          it!=_blockCols[i].end(); ++it){
        int pj=pinv[it->first];

        const typename SparseBlockMatrix<MatrixType>::SparseMatrixBlock* s=it->second;

        typename SparseBlockMatrix<MatrixType>::SparseMatrixBlock* b=0;
        if (! upperTriangle || pj<=pi) {
          b=dest->block(pj,pi,true);
          assert(b->cols()==s->cols());
          assert(b->rows()==s->rows());
          *b=*s;
        } else {
          b=dest->block(pi,pj,true);
          assert(b);
          assert(b->rows()==s->cols());
          assert(b->cols()==s->rows());
          *b=s->transpose();
        }
      }
      //cerr << endl;
      // within each row, 
    }
    return true;
    
  }

  template <class MatrixType>
  int SparseBlockMatrix<MatrixType>::fillCCS(double* Cx, bool upperTriangle) const
  {
    assert(Cx && "Target destination is NULL");
    double* CxStart = Cx;
    for (size_t i=0; i<_blockCols.size(); ++i){
      int cstart=i ? _colBlockIndices[i-1] : 0;
      int csize=colsOfBlock(i);
      for (int c=0; c<csize; ++c) {
        for (typename SparseBlockMatrix<MatrixType>::IntBlockMap::const_iterator it=_blockCols[i].begin(); it!=_blockCols[i].end(); ++it){
          const typename SparseBlockMatrix<MatrixType>::SparseMatrixBlock* b=it->second;
          int rstart=it->first ? _rowBlockIndices[it->first-1] : 0;

          int elemsToCopy = b->rows();
          if (upperTriangle && rstart == cstart)
            elemsToCopy = c + 1;
          memcpy(Cx, b->data() + c*b->rows(), elemsToCopy * sizeof(double));
          Cx += elemsToCopy;

        }
      }
    }
    return Cx - CxStart;
  }

  template <class MatrixType>
  int SparseBlockMatrix<MatrixType>::fillCCS(int* Cp, int* Ci, double* Cx, bool upperTriangle) const
  {
    assert(Cp && Ci && Cx && "Target destination is NULL");
    int nz=0;
    for (size_t i=0; i<_blockCols.size(); ++i){
      int cstart=i ? _colBlockIndices[i-1] : 0;
      int csize=colsOfBlock(i);
      for (int c=0; c<csize; ++c) {
        *Cp=nz;
        for (typename SparseBlockMatrix<MatrixType>::IntBlockMap::const_iterator it=_blockCols[i].begin(); it!=_blockCols[i].end(); ++it){
          const typename SparseBlockMatrix<MatrixType>::SparseMatrixBlock* b=it->second;
          int rstart=it->first ? _rowBlockIndices[it->first-1] : 0;

          int elemsToCopy = b->rows();
          if (upperTriangle && rstart == cstart)
            elemsToCopy = c + 1;
          for (int r=0; r<elemsToCopy; ++r){
            *Cx++ = (*b)(r,c);
            *Ci++ = rstart++;
            ++nz;
          }
        }
        ++Cp;
      }
    }
    *Cp=nz;
    return nz;
  }

  template <class MatrixType>
  void SparseBlockMatrix<MatrixType>::fillBlockStructure(MatrixStructure& ms) const
  {
    int n     = _colBlockIndices.size();
    int nzMax = (int)nonZeroBlocks();

    ms.alloc(n, nzMax);
    ms.m = _rowBlockIndices.size();

    int nz = 0;
    int* Cp = ms.Ap;
    int* Ci = ms.Aii;
    for (int i = 0; i < static_cast<int>(_blockCols.size()); ++i){
      *Cp = nz;
      const int& c = i;
      for (typename SparseBlockMatrix<MatrixType>::IntBlockMap::const_iterator it=_blockCols[i].begin(); it!=_blockCols[i].end(); ++it) {
        const int& r = it->first;
        if (r <= c) {
          *Ci++ = r;
          ++nz;
        }
      }
      Cp++;
    }
    *Cp=nz;
    assert(nz <= nzMax);
  }

  template <class MatrixType>
  bool SparseBlockMatrix<MatrixType>::writeOctave(const char* filename, bool upperTriangle) const
  {
    std::string name = filename;
    std::string::size_type lastDot = name.find_last_of('.');
    if (lastDot != std::string::npos) 
      name = name.substr(0, lastDot);

    std::vector<TripletEntry> entries;
    for (size_t i = 0; i<_blockCols.size(); ++i){
      const int& c = i;
      for (typename SparseBlockMatrix<MatrixType>::IntBlockMap::const_iterator it=_blockCols[i].begin(); it!=_blockCols[i].end(); ++it) {
        const int& r = it->first;
        const MatrixType& m = *(it->second);
        for (int cc = 0; cc < m.cols(); ++cc)
          for (int rr = 0; rr < m.rows(); ++rr) {
            int aux_r = rowBaseOfBlock(r) + rr;
            int aux_c = colBaseOfBlock(c) + cc;
            entries.push_back(TripletEntry(aux_r, aux_c, m(rr, cc)));
            if (upperTriangle && r != c) {
              entries.push_back(TripletEntry(aux_c, aux_r, m(rr, cc)));
            }
          }
      }
    }

    int nz = entries.size();
    std::sort(entries.begin(), entries.end(), TripletColSort());

    std::ofstream fout(filename);
    fout << "# name: " << name << std::endl;
    fout << "# type: sparse matrix" << std::endl;
    fout << "# nnz: " << nz << std::endl;
    fout << "# rows: " << rows() << std::endl;
    fout << "# columns: " << cols() << std::endl;
    fout << std::setprecision(9) << std::fixed << std::endl;

    for (std::vector<TripletEntry>::const_iterator it = entries.begin(); it != entries.end(); ++it) {
      const TripletEntry& entry = *it;
      fout << entry.r+1 << " " << entry.c+1 << " " << entry.x << std::endl;
    }
    return fout.good();
  }

  template <class MatrixType>
  int SparseBlockMatrix<MatrixType>::fillSparseBlockMatrixCCS(SparseBlockMatrixCCS<MatrixType>& blockCCS) const
  {
    blockCCS.blockCols().resize(blockCols().size());
    int numblocks = 0;
    for (size_t i = 0; i < blockCols().size(); ++i) {
      const IntBlockMap& row = blockCols()[i];
      typename SparseBlockMatrixCCS<MatrixType>::SparseColumn& dest = blockCCS.blockCols()[i];
      dest.clear();
      dest.reserve(row.size());
      for (typename IntBlockMap::const_iterator it = row.begin(); it != row.end(); ++it) {
        dest.push_back(typename SparseBlockMatrixCCS<MatrixType>::RowBlock(it->first, it->second));
        ++numblocks;
      }
    }
    return numblocks;
  }

  template <class MatrixType>
  int SparseBlockMatrix<MatrixType>::fillSparseBlockMatrixCCSTransposed(SparseBlockMatrixCCS<MatrixType>& blockCCS) const
  {
    blockCCS.blockCols().clear();
    blockCCS.blockCols().resize(_rowBlockIndices.size());
    int numblocks = 0;
    for (size_t i = 0; i < blockCols().size(); ++i) {
      const IntBlockMap& row = blockCols()[i];
      for (typename IntBlockMap::const_iterator it = row.begin(); it != row.end(); ++it) {
        typename SparseBlockMatrixCCS<MatrixType>::SparseColumn& dest = blockCCS.blockCols()[it->first];
        dest.push_back(typename SparseBlockMatrixCCS<MatrixType>::RowBlock(i, it->second));
        ++numblocks;
      }
    }
    return numblocks;
  }

  template <class MatrixType>
  void SparseBlockMatrix<MatrixType>::takePatternFromHash(SparseBlockMatrixHashMap<MatrixType>& hashMatrix)
  {
    // sort the sparse columns and add them to the map structures by
    // exploiting that we are inserting a sorted structure
    typedef std::pair<int, MatrixType*> SparseColumnPair;
    typedef typename SparseBlockMatrixHashMap<MatrixType>::SparseColumn HashSparseColumn;
    for (size_t i = 0; i < hashMatrix.blockCols().size(); ++i) {
      // prepare a temporary vector for sorting
      HashSparseColumn& column = hashMatrix.blockCols()[i];
      if (column.size() == 0)
        continue;
      std::vector<SparseColumnPair> sparseRowSorted; // temporary structure
      sparseRowSorted.reserve(column.size());
      for (typename HashSparseColumn::const_iterator it = column.begin(); it != column.end(); ++it)
        sparseRowSorted.push_back(*it);
      std::sort(sparseRowSorted.begin(), sparseRowSorted.end(), CmpPairFirst<int, MatrixType*>());
      // try to free some memory early
      HashSparseColumn aux;
      swap(aux, column);
      // now insert sorted vector to the std::map structure
      IntBlockMap& destColumnMap = blockCols()[i];
      destColumnMap.insert(sparseRowSorted[0]);
      for (size_t j = 1; j < sparseRowSorted.size(); ++j) {
        typename SparseBlockMatrix<MatrixType>::IntBlockMap::iterator hint = destColumnMap.end();
        --hint; // cppreference says the element goes after the hint (until C++11)
        destColumnMap.insert(hint, sparseRowSorted[j]);
      }
    }
  }

}// end namespace