[petsc-dev] MATOP_MAT_MULT

[Stefano Zampini]

> 
> 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 <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 <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)
> 
> 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/ <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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