[petsc-dev] MATOP_MAT_MULT

[Jose E. Roman]

I agree with Pierre and Stefano.
Hong: your proposed solution would be fine, but MATOP_MATPRODUCT does not exist yet, so I cannot try it.
I would like a solution along the lines of what Stefano suggests. It is not too much trouble if it goes to master instead of maint.

Thanks.
Jose


> El 22 abr 2020, a las 15:26, Stefano Zampini <stefano.zampini at gmail.com> escribió:
> 
> 
>> 
>> MatProductCreateWithMat(A,Vmat,NULL,Wmat);
>> MatProductSetType(Wmat,MATPRODUCT_AB);
>> MatHasOperation(Wmat,MATOP_MATPRODUCT,&flg); //new support, it calls MatProductSetFromOptions(Wmat)
> 
> Hong, this would go in the direction I was outlining here https://gitlab.com/petsc/petsc/-/issues/608
> How about also adding something like
> 
> MatProductIsImplemented(Wmat,&flg)
> 
> That returns true if a specific implementation is available? This way
> 
> This way, if we use both queries, we can assess the presence of the basic fallbacks too, i.e.
>  
> MatHasOperation(Wmat,MATOP_MATPRODUCT,&flg1)
> MatProductIsImplemented(Wmat,&flg2)
> 
> If flg1 is false, no support at all
> If flg1 is true and flg2 is false -> Basic implementation (i.e, MatShell with products inside)
> If flg1 and flg2 are both true -> Specific implementation available.
> 
>> 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
>> > 
>