[petsc-dev] MATOP_MAT_MULT

Pierre Jolivet pierre.jolivet at enseeiht.fr
Wed Apr 22 15:08:56 CDT 2020 

Hong,
I also now just tested some previously PETSC_VERSION_LT(3,13,0) running code with C=A*B, Dense=Nest*Dense, all previously allocated prior to a call to MatMatMult and scall = MAT_REUSE_MATRIX.
Sadly, it’s now broken. It is my fault for not having a test for this in https://gitlab.com/petsc/petsc/-/merge_requests/2069 <https://gitlab.com/petsc/petsc/-/merge_requests/2069>, sorry about that.
[0]PETSC ERROR: Call MatProductSymbolic() first
[0]PETSC ERROR: #1 MatProductNumeric() line 730 in /ccc/work/cont003/rndm/rndm/petsc/src/mat/interface/matproduct.c
[0]PETSC ERROR: #2 MatMatMult() line 9335 in /ccc/work/cont003/rndm/rndm/petsc/src/mat/interface/matrix.c

Here is a reproducer (that will work OK with 3.12.4).
diff --git a/src/mat/tests/ex195.c b/src/mat/tests/ex195.c
index c72662bc3c..811de669c5 100644
--- a/src/mat/tests/ex195.c
+++ b/src/mat/tests/ex195.c
@@ -73,2 +73,3 @@ int main(int argc,char **args)
   ierr = MatMatMult(nest,B,MAT_REUSE_MATRIX,PETSC_DEFAULT,&C);CHKERRQ(ierr);
+  ierr = MatMatMult(nest,C,MAT_REUSE_MATRIX,PETSC_DEFAULT,&B);CHKERRQ(ierr);
   ierr = MatMatMultEqual(nest,B,C,10,&equal);CHKERRQ(ierr);

$ make -f gmakefile test searchin=mat_tests-ex195

I believe this is very close to the topic at hand and issue #608, so maybe you could fix this as well in the same upcoming MR? Just let me know, I can have a crack it otherwise.
Thanks,
Pierre

> On 22 Apr 2020, at 5:38 PM, Zhang, Hong <hzhang at mcs.anl.gov> wrote:
> 
> Jose, Pierre and Stefano,
> Now I understand the issue that Stefano raised. I plan to add
> MatProductIsSupported(Wmat,&supported,&matproductsetfromoptions)
> the flag 'supported' tells if the product is supported/implemented or not,
> and the function pointer 'matproductsetfromoptions' gives the name of MatProductSetFromOptions_xxx, (including basic implementation) or NULL.
> 
> Let me know your suggestions. I'll list all of you as reviewer.
> Hong
> 
> From: Jose E. Roman <jroman at dsic.upv.es>
> Sent: Wednesday, April 22, 2020 9:07 AM
> To: Stefano Zampini <stefano.zampini at gmail.com>
> Cc: Zhang, Hong <hzhang at mcs.anl.gov>; Pierre Jolivet <pierre.jolivet at enseeiht.fr>; petsc-dev <petsc-dev at mcs.anl.gov>
> Subject: Re: [petsc-dev] MATOP_MAT_MULT
>  
> 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 <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
> >> > (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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