[petsc-dev] MatTransposeMatMult

[Jed Brown]

~jedbrown/ceres_solver_iteration_001_A.petsc on mcs.anl.gov.

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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