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

From: Marco Caliari
Subject: Re: Mark a matrix "upper" in a oct-file
Date: Tue, 9 Sep 2014 13:16:44 +0200 (CEST)
User-agent: Alpine 2.10 (DEB 1266 2009-07-14)

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 

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 

Dear all, copying from, 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, 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.



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