[petsc-users] Is this a bug? MatMultAdd_SeqBAIJ_11

[Matthew Knepley]

On Tue, Sep 21, 2021 at 10:04 AM Barry Smith <bsmith at petsc.dev> wrote:

>
>    Daniel,
>
>      Thanks for the update. We can patch the release version of PETSc
> (normally we don't have a way to patch previous release versions)
>
>      There is no direct option to always use the _N version. (For smaller
> blocks using _N is very slow).
>

It is in an MR: https://gitlab.com/petsc/petsc/-/merge_requests/4338

  Thanks,

     Matt


>     Barry
>
>
> On Sep 21, 2021, at 9:51 AM, Daniel Stone <daniel.stone at opengosim.com>
> wrote:
>
> I seem to have confirmed that making the change suggested by Lawrence
> fixes things in our
> case. Some alternate runs by a colleague that result in a blocksize 12
> matrix also work
> fine - I think in that case MAtMultAdd_SeqBAIJ_N must be being used as I
> can't find
> a blocksize 12 analogue.
>
> Is there by any chance a setting somewhere that can tell petsc to override
> the use of
> blocksize specific routines like this and always go to, e.g.,
> MatMultAdd_SeqBAIJ_N
> etc? Might be useful as a short term fix.
>
> Thanks,
>
> Daniel
>
> On Tue, Sep 21, 2021 at 11:50 AM Lawrence Mitchell <wence at gmx.li> wrote:
>
>> Hi Daniel,
>>
>> > On 21 Sep 2021, at 11:19, Daniel Stone <daniel.stone at opengosim.com>
>> wrote:
>> >
>> > Hello,
>> >
>> > If we look at lines 2330-2331 in file baij2.c, it looks like there are
>> some
>> > mistakes in assigning the `sum..` variables to the z array, causing
>> > the function MatMultAdd_SeqBAIJ_11() to not produce the correct
>> > answer.
>> >
>> > I don't have a good example program to demonstrate this yet - it's
>> > currently causing problems in a dev branch of pflotan_ogs that
>> > can produce blocksize 11 matrices. When in parallel, a standard
>> > matrix-vector multiplication calls MatMultAdd for the off-proc
>> > contributions, and the result is wrong when this is redirected
>> > to MatMultAdd_SeqBAIJ_11. Seems to be the root cause of
>> > several solvers failing such as fgmres.
>> >
>> > Can anyone confirm that these two lines seem incorrect?
>>
>> Looks wrong to me, I guess this patch is correct?
>>
>> diff --git a/src/mat/impls/baij/seq/baij2.c
>> b/src/mat/impls/baij/seq/baij2.c
>> index 2849ef9051..65513c8989 100644
>> --- a/src/mat/impls/baij/seq/baij2.c
>> +++ b/src/mat/impls/baij/seq/baij2.c
>> @@ -2328,7 +2328,7 @@ PetscErrorCode MatMultAdd_SeqBAIJ_11(Mat A,Vec
>> xx,Vec yy,Vec zz)
>>        v    += 121;
>>      }
>>      z[0] = sum1; z[1] = sum2; z[2] = sum3; z[3] = sum4; z[4] = sum5;
>> z[5] = sum6; z[6] = sum7;
>> -    z[7] = sum6; z[8] = sum7; z[9] = sum8; z[10] = sum9; z[11] = sum10;
>> +    z[7] = sum8; z[8] = sum9; z[9] = sum10; z[10] = sum11;
>>      if (!usecprow) {
>>        z += 11; y += 11;
>>      }
>>
>>
>> Lawrence
>
>
>

-- 
What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to which their
experiments lead.
-- Norbert Wiener

https://www.cse.buffalo.edu/~knepley/ <http://www.cse.buffalo.edu/~knepley/>
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