[petsc-dev] MATOP_MAT_MULT

[Pierre Jolivet]

> On 21 Apr 2020, at 5:22 PM, Zhang, Hong <hzhang at mcs.anl.gov> wrote:
> 
> Pierre,
> MatMatMult_xxx() is removed from MatOps table.

Shouldn’t there be a deprecation notice somewhere?
There is nothing about MATOP_MAT_MULT in the 3.13 changelog https://www.mcs.anl.gov/petsc/documentation/changes/313.html <https://www.mcs.anl.gov/petsc/documentation/changes/313.html>
For example, I see that in SLEPc, José is currently making these checks, which are in practice useless as they always return PETSC_FALSE? https://gitlab.com/slepc/slepc/-/blob/master/src/sys/classes/bv/impls/contiguous/contig.c#L191 <https://gitlab.com/slepc/slepc/-/blob/master/src/sys/classes/bv/impls/contiguous/contig.c#L191>
(Maybe José is aware of this and this is just for testing)

> MatMatMult() is replaced by
> MatProductCreate()
> MatProductSetType(,MATPRODUCT_AB)
> MatProductSetFromOptions()
> MatProductSymbolic()
> MatProductNumeric()
> 
> Where/when do you need query a single matrix for its product operation?

I didn’t want to bother at first with the new API, because I’m only interested in C = A*B with C and B being dense.
Of course, I can update my code, but if I understand Stefano’s issue correctly, and let’s say my A is of type SBAIJ, for which there is no MatMatMult, the code will now error out in the MatProduct?
There is no fallback mechanism? Meaning I could in fact _not_ use the new API and will just have to loop on all columns of B, even for AIJ matrices.

Thanks,
Pierre

> Hong
> 
> From: petsc-dev <petsc-dev-bounces at mcs.anl.gov> on behalf of Pierre Jolivet <pierre.jolivet at enseeiht.fr>
> Sent: Tuesday, April 21, 2020 7:50 AM
> To: petsc-dev <petsc-dev at mcs.anl.gov>
> Subject: [petsc-dev] MATOP_MAT_MULT
>  
> Hello,
> Am I seeing this correctly?
> #include <petsc.h>
> 
> int main(int argc,char **args)
> {
>   Mat               A;
>   PetscBool         hasMatMult;
>   PetscErrorCode    ierr;
> 
>   ierr = PetscInitialize(&argc,&args,NULL,NULL);if (ierr) return ierr;
>   ierr = MatCreate(PETSC_COMM_WORLD,&A);CHKERRQ(ierr);
>   ierr = MatSetType(A,MATMPIAIJ);CHKERRQ(ierr);
>   ierr = MatHasOperation(A,MATOP_MAT_MULT,&hasMatMult);CHKERRQ(ierr);
>   printf("%s\n", PetscBools[hasMatMult]);
>   ierr = PetscFinalize();
>   return ierr;
> }
> 
> => FALSE
> 
> I believe this is a regression (or at least an undocumented change) introduced here: https://gitlab.com/petsc/petsc/-/merge_requests/2524/ <https://gitlab.com/petsc/petsc/-/merge_requests/2524/>
> I also believe Stefano raised a similar point there: https://gitlab.com/petsc/petsc/-/issues/608 <https://gitlab.com/petsc/petsc/-/issues/608>
> This is a performance killer in my case because I was previously using this check to know whether I could use MatMatMult or had to loop on all columns and call MatMult on all of them.
> There is also a bunch of (previously functioning but now) broken code, e.g., https://www.mcs.anl.gov/petsc/petsc-current/src/mat/impls/transpose/transm.c.html#line105 <https://www.mcs.anl.gov/petsc/petsc-current/src/mat/impls/transpose/transm.c.html#line105> or https://www.mcs.anl.gov/petsc/petsc-current/src/mat/impls/nest/matnest.c.html#line2105 <https://www.mcs.anl.gov/petsc/petsc-current/src/mat/impls/nest/matnest.c.html#line2105>
> Is this being addressed/documented?
> 
> Thanks,
> Pierre

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