Re: [eigen] Copy into a MappedSparseMatrix

[Norman Goldstein <normvcr@xxxxxxxxx>]

My version of Eigen is 3.2.4, so I think I need to use 
MappedSparseMatrix, for now.

I wrote the following method that works, based on your std::copy() 
suggestion:

namespace Eigen {

  template< typename _Scalar, int _Flags, typename _Index>
  MappedSparseMatrix< _Scalar, _Flags, _Index >&
  copy( const SparseMatrix< _Scalar, _Flags, _Index >& src,
    MappedSparseMatrix< _Scalar, _Flags, _Index >& dest )
  {
    assert( src.isCompressed() );

    // The Flags already match for row/column major
    assert( dest.rows() == src.rows() &&
        dest.cols() == src.cols() &&
        dest.nonZeros() == src.nonZeros() );

    std::copy( src.valuePtr(),
           src.valuePtr() + src.nonZeros(),
           dest.valuePtr() );

    std::copy( src.innerIndexPtr(),
           src.innerIndexPtr() + src.nonZeros(),
           dest.innerIndexPtr() );

    std::copy( src.outerIndexPtr(),
           src.outerIndexPtr() + 1 + src.outerSize(),
           dest.outerIndexPtr() );

    return dest;
  }// operator=( MappedSparseMatrix, SparseMatrix )
}

So,  copy( a, b ) works, but copy( a*b, c ) does not work.  I get the

-------------------------------
 error: no matching function for call to
 ‘copy(const Type, Eigen::MappedSparseMatrix<double, 1>&)’
       Eigen::copy( jmat.transpose() * jmat, hmat );
                                                  ^
 note: candidate is:
 note: template<class _Scalar, int _Flags, class _Index> 
Eigen::MappedSparseMatrix<_Scalar, _Flags, _Index>&
Eigen::copy(const Eigen::SparseMatrix<_Scalar, _Options, _Index>&, 
Eigen::MappedSparseMatrix<_Scalar, _Flags, _Index>&)
   copy( const SparseMatrix< _Scalar, _Flags, _Index >& src,
   ^
: note:   ‘const Type {aka const Eigen::SparseSparseProduct<const 
Eigen::Transpose<Eigen::MappedSparseMatrix<double, 1> >, 
Eigen::SparseMatrix<double, 0, int> >}’ is not derived from ‘const 
Eigen::SparseMatrix<_Scalar, _Options, _Index>’
       Eigen::copy( jmat.transpose() * jmat, hmat );
-------------------------------

Could I have coded copy() in such a way to include SparseSparseProduct
as well as SparseMatrix as the src argument to copy?


Thanks.

On 07/16/2015 04:38 AM, Christoph Hertzberg wrote:
> On 16.07.2015 at 07:35, Norman Goldstein wrote:
> > I have the following two matices:
> >
> > MappedSparseMatrix<...> hmat;  // Points to some data off to the side
>
> MappedSparseMatrix is deprecated, you should use Map<SparseMatrix<...> >
>
>
> > SparseMatrix<...> prod;                 // Contains data, same size and
> > structure as hmat
> >
> > I want to copy the prod data over to where hmat is pointing:
> >
> > hmat = prod;
>
> I'm not sure that this is a good idea (what behavior would you expect, 
> if the structure does not match?). If you are certain that the 
> structure is the same, you could directly copy the contents of 
> prod.valuePtr() to hmat.valuePtr() (using std::copy).
>
>
> Christoph