[petsc-dev] MatTransposeMatMult

Hong hzhang at mcs.anl.gov
Thu Sep 21 09:59:29 CDT 2017

Jed :

> ~jedbrown/ceres_solver_iteration_001_A.petsc on mcs.anl.gov.
I got this file. How many  matrices in this file? How to load them?
It seems the first matrix is rectangular.


> The issue is that MatTransposeMatMult is implemented using sparse outer
> products which is quite inefficient compared to the standard MatMatMult
> algorithm.
> Barry Smith <bsmith at mcs.anl.gov> writes:
> >   Send the runable case so that we can determine the cause of the slow
> down and find possible cures. It could be that the "optimized" version was
> optimized for a particular size of problems or matrix structure.
> >
> >    Barry
> >
> >> On Sep 20, 2017, at 4:32 PM, Jed Brown <jed at jedbrown.org> wrote:
> >>
> >> I have a simple SeqAIJ example where MatTransposeMatMult is 30x slower
> >> than MatTranspose followed by MatMatMult.  This is embarrassing when
> >> people try to compare performance.  Are there any cases where these
> >> custom implementations provide value rather than just confusing people
> >> or turning them away from PETSc?
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