[petsc-dev] Problems with MatGetSubMatrices_SeqSBAIJ

[Hong]

Alejandro:
I can reproduce this error. I'm investigating it.

I made minor update of MatGetSubMatrices_SeqSBAIJ() in v3.7 which only
removed requirement of isrow=iscol...do not know what leads to this error
yet.

Hong

Hi,
>
> After updating petsc from version 3.6.2 to 3.7, I had the following
> problem:
>
> The result that I get from doing something like
> MatMult(schurComplement,v1,v2); differs between the petsc versions that I
> mentioned. I traced back the problem to the function
> MatGetSubMatrices_SeqSBAIJ(). What I did in order to temporarily solve my
> problem was to use in petsc 3.7 the code of MatGetSubMatrices_SeqSBAIJ()
> corresponding to petsc 3.6.2.
>
> How I solved the problem is not a real solution, but it allows me to keep
> working. My question is: is it a bug or do you think that there could be
> something wrong with my code from which I use petsc?
>
> I think it should be a bug. If I run the ksp example 59 which uses FETI-DP
> (whose implementation also uses something like
> MatMult(schurComplement,v1,v2)) with petsc 3.7, I get the following
> unexpected answer
>
> mpiexec -n 4 ./ex59 -npx 2 -npy 2 -nex 60 -ney 60 -ksp_max_it 3
> ------------------FETI-DP stats-------------------------------
> Number of degrees of freedom               :      355
> Number of iterations                       :        3
> Eigenvalues preconditioned operator        : 1.49e+00 8.86e+00
> Error betweeen exact and computed solution : 1.91e+00
> --------------------------------------------------------------
>
> If I run the same problem with petsc 3.7 but with
> MatGetSubMatrices_SeqSBAIJ() corresponding to petsc 3.6.2, I get the
> expected answer
>
> mpiexec -n 4 ./ex59 -npx 2 -npy 2 -nex 60 -ney 60 -ksp_max_it 3
> ------------------FETI-DP stats-------------------------------
> Number of degrees of freedom               :      355
> Number of iterations                       :        3
> Eigenvalues preconditioned operator        : 1.08e+00 2.08e+00
> Error betweeen exact and computed solution : 3.60e-02
> --------------------------------------------------------------
>
>
> Thanks,
> Alejandro
>
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