Re: Mark a matrix "upper" in a oct-file

[Marco Caliari]

On Fri, 5 Sep 2014, David Bateman wrote:

> > Le 5 sept. 2014 à 13:56, Marco Caliari <address@hidden> a écrit :
> >
> > Dear all,
> >
> > I have to take the upper triangular part of a matrix in a oct-file. Later, I 
> > have to perform RowVector-Matrix products with it. This is my code
> >
> > // given Matrix F(m,m)
> > // take the upper triangular part
> > for (octave_idx_type j = 0; j < m; j++)
> >    {
> >      for (octave_idx_type i = j+1; i < m; i++)
> >    F(i,j) = 0.0;
> >    }
> >  RowVector d = F.row(0);
> > // make RowVector-matrix products
> >  for (octave_idx_type i = 0; i < s-1; i++)
> >    d = d * F;
> >
> > My question is: if I mark the matrix "upper" (but do not know how to do it), is 
> > the RowVector-Matrix product faster (for instance BLAS dtrmv is used instead of general 
> > dgemv)?
>
> Look at the matrix_type function for how to mark the matrix as upper. However, 
> marking it as such is only useful at this point for the solve function or slash 
> operators.

Dear all, copying from dMatrix.cc, I replaced

for (octave_idx_type i = 0; i < s-1; i++)
  d = d*F

with the triangular matrix vector product

double *Fd = d.fortran_vec();
for (octave_idx_type i = 0; i < s-1; i++)
     {
      F77_XFCN(dtrmv, DTRMV, (F77_CONST_CHAR_ARG2 ("U",1),
                              F77_CONST_CHAR_ARG2 ("T",1),
                              F77_CONST_CHAR_ARG2 ("N",1),
                              m, F.data(),
                              m, Fd, 1
                              F77_CHAR_ARG_LEN (1)
                              F77_CHAR_ARG_LEN (1)
                              F77_CHAR_ARG_LEN (1)));
                              }


It works, but even with large matrices (around 400x400) I do not see any 
speed-up.

Thanks,

Marco