[petsc-users] MatCreateSubMatricesMPI strange behavior

[Mark Adams]

First, you can not mix communicators in PETSc calls in general (ever?), but
this error looks like you might be asking for a row from the matrix
that does not exist.
You should start with a PETSc example code. Test it and modify it to suit
your needs.

Good luck,
Mark

On Fri, Jul 25, 2025 at 9:31 AM Alexis SALZMAN <alexis.salzman at ec-nantes.fr>
wrote:

> Hi,
>
> As I am relatively new to Petsc, I may have misunderstood how to use the
> MatCreateSubMatricesMPI function. The attached code is tuned for three
> processes and extracts one matrix for each colour of a subcommunicator
> that has been created using the MPI_Comm_split function from an  MPIAij
> matrix. The following error message appears when the code is set to its
> default configuration (i.e. when a rectangular matrix is extracted with
> more rows than columns for colour 0):
>
> [0]PETSC ERROR: --------------------- Error Message
> --------------------------------------------------------------
> [0]PETSC ERROR: Argument out of range
> [0]PETSC ERROR: Column too large: col 4 max 3
> [0]PETSC ERROR: See
> https://urldefense.us/v3/__https://petsc.org/release/faq/__;!!G_uCfscf7eWS!ZqH097BZ0G0O3WI7RWrwIKFNpyk0czSWEqfusAeTlgEygAffwpgBUzsLw1TIoGkjZ3mYG-NRQxxFoxU4y8EyY0ofiz9I43Qwe0w$
> for trouble shooting.
> [0]PETSC ERROR: Petsc Release Version 3.22.2, unknown
>
> ... petsc git hash 2a89477b25f compiled on a dell i9 computer with Gcc
> 14.3, mkl 2025.2, .....
> [0]PETSC ERROR: #1 MatSetValues_SeqAIJ() at
> ...petsc/src/mat/impls/aij/seq/aij.c:426
> [0]PETSC ERROR: #2 MatSetValues() at
> ...petsc/src/mat/interface/matrix.c:1543
> [0]PETSC ERROR: #3 MatSetSeqMats_MPIAIJ() at
> .../petsc/src/mat/impls/aij/mpi/mpiov.c:2965
> [0]PETSC ERROR: #4 MatCreateSubMatricesMPI_MPIXAIJ() at
> .../petsc/src/mat/impls/aij/mpi/mpiov.c:3163
> [0]PETSC ERROR: #5 MatCreateSubMatricesMPI_MPIAIJ() at
> .../petsc/src/mat/impls/aij/mpi/mpiov.c:3196
> [0]PETSC ERROR: #6 MatCreateSubMatricesMPI() at
> .../petsc/src/mat/interface/matrix.c:7293
> [0]PETSC ERROR: #7 main() at sub.c:169
>
> When the '-ok' option is selected, the code extracts a square matrix for
> colour 0, which runs smoothly in this case. Selecting the '-trans'
> option swaps the row and column selection indices, providing a
> transposed submatrix smoothly. For colour 1, which uses only one process
> and is therefore sequential, rectangular extraction is OK regardless of
> the shape.
>
> Is this dependency on the shape expected? Have I missed an important
> tuning step somewhere?
>
> Thank you in advance for any clarification.
>
> Regards
>
> A.S.
>
> P.S.: I'm sorry, but as I'm leaving my office for the following weeks
> this evening, I won't be very responsive during this period.
>
>
>
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