[petsc-users] Newbie Question - Really slow - PetscMemCpy

Matthew Knepley knepley at gmail.com
Thu Apr 22 10:11:52 CDT 2010

On Thu, Apr 22, 2010 at 9:22 AM, Jed Brown <jed at 59a2.org> wrote:

> On Thu, 22 Apr 2010 15:15:12 +0100, "Parker, Andrew (UK Filton)" <
> Andrew.Parker2 at baesystems.com> wrote:
> > Well that's a worry, no error from:
> >
> > Still slow as hell, same behaviour as before.  I'm now using:
> >
> >   MatCreate(PETSC_COMM_SELF,&_storage);
> >   MatSetType(_storage, MATSEQBAIJ);
> >
> > MatSetSizes(_storage,PETSC_DECIDE,PETSC_DECIDE,numVars*numLocs,numVars*n
> > umLocs);
> >   MatSetFromOptions(_storage);
> >   MatSeqBAIJSetPreallocation(_storage,numVars,PETSC_NULL,sparsityStart);

Then there is something wrong in your code at large that we cannot
see from this small snippet. Can you change a PETSc example into
something that exhibits this behavior, like KSP ex2?

Also, you can go in with the debugger and see what is happening. I am
you switch the matrix you are using (so options do not take effect), or
it, etc.


> This should work if you call both MatSetSizes and MatSetType before
> MatSetOption.  There are technical reasons for this, mostly that it's
> difficult to cache all the options and get them handled in a consistent
> and debuggable manner once the implementation is chosen.
> Unless someone disagrees, I'll make it an error to call MatSetOptions()
> before the implementation is available (so you would get a useful error
> with the usage above, instead of the option just being ignored).
> Jed

What most experimenters take for granted before they begin their experiments
is infinitely more interesting than any results to which their experiments
-- Norbert Wiener
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