[Boost-users] access to boost spars matrix values

From: Franck Perignon (Franck.Perignon_at_[hidden])
Date: 2006-10-09 05:10:52

Good morning,

Can somebody help me using sparse matrices? Here is my problem:

I have a class, named MySimpleMatrix, whith a private member, mat, of 
type MyMat which is a union of
various boost matrices type:

      typedef matrix<double, row_major,std::vector<double> > DenseMat;
      typedef triangular_matrix<double, upper, row_major,
      std::vector<double> > TriangMat;
      ...
      typedef mapped_matrix<double> SparseMat;
      ...

      union MyMat{
        DenseMat *Dense;      TriangMat *Triang;
        SymMat *Sym;
        SparseMat *Sparse;
        BandedMat *Banded;
      };

      class MySimpleMatrix
      {
       private:
        unsigned int num;
        MyMat mat;
      ...
      }

num =1, means mat is a dense, 2 a triangular and so on.

the operator () is overloaded in the following way:

   double& MySimpleMatrix::operator () (unsigned int row, unsigned
   int col)
      {
      ...
        switch(num){
        case 1:
          return (*mat.Dense)(row,col);
          break;
      ...
        case 4:
          return (*mat.Sparse)(row,col);
          break;
      ...
        }
      }

It works for all matrices types, except sparse where it fails with this 
message:
error: invalid initialization of non-const reference of type 'double&' 
from a temporary of type 
'boost::numeric::ublas::sparse_matrix_element<boost::numeric::ublas::mapped_matrix<double, 
boost::numeric::ublas::basic_row_major<unsigned int, int>, 
boost::numeric::ublas::map_std<unsigned int, double, 
std::allocator<std::pair<const unsigned int, double> > > > >'

I undersand I need to get a reference to double as a return value, which 
is not given by (*mat.Sparse)(row,col), and thus my question is how to 
get the good type from mat.sparse to make my operator work??

Thanks,
F.Perignon