[petsc-dev] MATOP_MAT_MULT

[Zhang, Hong]

Jose,
We need both A and Vmat to determine if Wmat= A*Vmat is supported or not.

MatHasOperation(A,MATOP_MAT_MULT,&flg); //this call is not sufficient to ensure Wmat.

How about replacing
  if (V->vmm && flg) {
    ierr = BVGetMat(V,&Vmat);CHKERRQ(ierr);
    ierr = BVGetMat(W,&Wmat);CHKERRQ(ierr);
    ierr = MatProductCreateWithMat(A,Vmat,NULL,Wmat);CHKERRQ(ierr);
    ierr = MatProductSetType(Wmat,MATPRODUCT_AB);CHKERRQ(ierr);
    ierr = MatProductSetFromOptions(Wmat);CHKERRQ(ierr);
    ierr = MatProductSymbolic(Wmat);CHKERRQ(ierr);
    ierr = MatProductNumeric(Wmat);CHKERRQ(ierr);
    ierr = BVRestoreMat(V,&Vmat);CHKERRQ(ierr);
    ierr = BVRestoreMat(W,&Wmat);CHKERRQ(ierr);
  } else {
    ...
  }


with

MatProductCreateWithMat(A,Vmat,NULL,Wmat);
MatProductSetType(Wmat,MATPRODUCT_AB);

MatHasOperation(Wmat,MATOP_MATPRODUCT,&flg); //new support, it calls MatProductSetFromOptions(Wmat)

if (V->vmm && flg) {

  MatProductSymbolic(Wmat);

  MatProductNumeric(Wmat);

} else {

  MatDestroy(Wmat);

...

}

Hong


________________________________
From: Jose E. Roman <jroman at dsic.upv.es>
Sent: Tuesday, April 21, 2020 11:21 AM
To: Pierre Jolivet <pierre.jolivet at enseeiht.fr>
Cc: Zhang, Hong <hzhang at mcs.anl.gov>; petsc-dev <petsc-dev at mcs.anl.gov>
Subject: Re: [petsc-dev] MATOP_MAT_MULT



> El 21 abr 2020, a las 17:53, Pierre Jolivet <pierre.jolivet at enseeiht.fr> escribió:
>
>
>
>> 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
> 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
> (Maybe José is aware of this and this is just for testing)

No, I was not aware of this. Thanks for bringing this up. Now in 3.13 we are always doing the slow version (column by column), so yes I am interested in a solution for this.

>
>> 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/
>> I also believe Stefano raised a similar point there: 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 or 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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