[GiNaC-list] (no subject) has to be: avoid expansion in
Javier Ros Ganuza
jros at unavarra.es
Thu Mar 9 11:07:23 CET 2006
Thanks for the different replies. I've got the idea.
I'm geting impressed with ginac. I'm using it to perform a rather simple
task, but I was unable to deal with it with matlab(symbolic) or maple,
due to their limitations in subs funtions.
Incredible fine piece of work!
On Wed, 2006-03-08 at 23:24 +0100, Richard B. Kreckel wrote:
> Sheplyakov Alexei wrote:
> >You can try this silly patch:
> >Index: ginac/matrix.cpp
> >RCS file: /home/cvs/GiNaC/ginac/matrix.cpp,v
> >retrieving revision 220.127.116.11
> >diff -u -r18.104.22.168 matrix.cpp
> >--- ginac/matrix.cpp 19 Oct 2005 21:21:56 -0000 22.214.171.124
> >+++ ginac/matrix.cpp 8 Mar 2006 18:51:06 -0000
> >@@ -583,7 +583,7 @@
> > if (m[r1*col+c].is_zero())
> > continue;
> > for (unsigned r2=0; r2<other.cols(); ++r2)
> >- prod[r1*other.col+r2] += (m[r1*col+c] * other.m[c*other.col+r2]).expand();
> >+ prod[r1*other.col+r2] += (m[r1*col+c] * other.m[c*other.col+r2]);
> > }
> > }
> > return matrix(row, other.col, prod);
> I think the expansion was unintentional and I have applied this patch to
> the trunk. Thanks.
> In matrix operations, in particularl in the elimination algorithms, one
> frequently needs to try a bit harder than if (foo.is_zero())... to test
> for zeros. One also needs to take some care to avoid excessively long
> terms to build up. For the elements of a matrix product, I see no need
> for the former, but I do see need for the latter. For instance,
> consider evalm([[(a+b),0],[0,(c+d)]]^666); in ginsh notation.
More information about the GiNaC-list