[petsc-users] question on PCLSC with matrix blocks of type MATNEST

[Zhang, Hong]

Pierre,
I just modified the error message of MatProductSymbolic() and added a testing segment in src/mat/tests/ex195.c. I have not pushed my change yet.

Your fix at https://gitlab.com/petsc/petsc/-/commit/9dcea022de3b0309e5c16b8c554ad9c85dea29cf?merge_request_iid=7283 is more general. Has this fix merged to release and main? With latest main and release, I get same previous error message.
Hong

________________________________
From: Pierre Jolivet <pierre at joliv.et>
Sent: Sunday, February 11, 2024 7:43 AM
To: Zhang, Hong <hzhang at mcs.anl.gov>
Cc: Hana Honnerová <hhornik at kma.zcu.cz>; petsc-users at mcs.anl.gov <petsc-users at mcs.anl.gov>
Subject: Re: [petsc-users] question on PCLSC with matrix blocks of type MATNEST


On 8 Feb 2024, at 5:37 PM, Zhang, Hong via petsc-users <petsc-users at mcs.anl.gov> wrote:

Hana,
"product AB with A nest, B nest" is not supported by PETSc. I do not know why PETSc does not display such an error message. I'll check it.

Did you?
A naive fix is to simply add the missing PetscCheck() in MatProduct_Private() right after MatProductSetFromOptions() https://petsc.org/release/src/mat/interface/matrix.c.html#line10026 (notice that it is there line 10048 in the other code branch)
I have this at https://gitlab.com/petsc/petsc/-/commit/9dcea022de3b0309e5c16b8c554ad9c85dea29cf?merge_request_iid=7283 (coupled with code refactoring to avoid missing any other operations), but maybe we could do things more elegantly.

Thanks,
Pierre

Hong
________________________________
From: petsc-users <petsc-users-bounces at mcs.anl.gov> on behalf of Hana Honnerová <hhornik at kma.zcu.cz>
Sent: Thursday, February 8, 2024 4:45 AM
To: petsc-users at mcs.anl.gov <petsc-users at mcs.anl.gov>
Subject: [petsc-users] question on PCLSC with matrix blocks of type MATNEST

Hi all,
I am trying to solve linear systems arising from isogeometric discretization (similar to FEM) of the Navier-Stokes equations in parallel using PETSc. The linear systems are of saddle-point type, so I would like to use the PCFIELDSPLIT preconditioner with the -pc_fieldsplit_detect_saddle_point option, Schur complement factorization and the LSC Schur complement preconditioner. I do not provide any user-defined operators for PCLSC in my codes (at least for now).
I store the matrix as a MATNEST consisting of 4 blocks (F for velocity-velocity part, Bt for velocity-pressure part, B for pressure-velocity part and NULL for pressure-pressure part). It is also convenient for me to store the blocks F, Bt and B as another MATNEST consisting of blocks corresponding to individual velocity components.

However, in this setting, I get the following error message:
[0]PETSC ERROR: Petsc has generated inconsistent data
[0]PETSC ERROR: Unspecified symbolic phase for product AB with A nest, B nest. Call MatProductSetFromOptions() first
[0]PETSC ERROR: See https://petsc.org/release/faq/ for trouble shooting.
[0]PETSC ERROR: Petsc Release Version 3.20.4, unknown
[0]PETSC ERROR: /home/hhornik/gismo/build-petsc-mpi/RelWithDebInfo/bin/gsINSSolverPETScTest on a arch-debug named ThinkPad-T14 by hhornik Thu Feb  8 11:04:17 2024
[0]PETSC ERROR: Configure options PETSC_ARCH=arch-debug --with-debugging=1 --download-mumps --download-scalapack
[0]PETSC ERROR: #1 MatProductSymbolic() at /home/hhornik/Software/PETSc/src/mat/interface/matproduct.c:807
[0]PETSC ERROR: #2 MatProduct_Private() at /home/hhornik/Software/PETSc/src/mat/interface/matrix.c:10027
[0]PETSC ERROR: #3 MatMatMult() at /home/hhornik/Software/PETSc/src/mat/interface/matrix.c:10103
[0]PETSC ERROR: #4 PCSetUp_LSC() at /home/hhornik/Software/PETSc/src/ksp/pc/impls/lsc/lsc.c:79
[0]PETSC ERROR: #5 PCSetUp() at /home/hhornik/Software/PETSc/src/ksp/pc/interface/precon.c:1080
[0]PETSC ERROR: #6 KSPSetUp() at /home/hhornik/Software/PETSc/src/ksp/ksp/interface/itfunc.c:415
[0]PETSC ERROR: #7 KSPSolve_Private() at /home/hhornik/Software/PETSc/src/ksp/ksp/interface/itfunc.c:832
[0]PETSC ERROR: #8 KSPSolve() at /home/hhornik/Software/PETSc/src/ksp/ksp/interface/itfunc.c:1079
[0]PETSC ERROR: #9 PCApply_FieldSplit_Schur() at /home/hhornik/Software/PETSc/src/ksp/pc/impls/fieldsplit/fieldsplit.c:1165
[0]PETSC ERROR: #10 PCApply() at /home/hhornik/Software/PETSc/src/ksp/pc/interface/precon.c:498
[0]PETSC ERROR: #11 KSP_PCApply() at /home/hhornik/Software/PETSc/include/petsc/private/kspimpl.h:383
[0]PETSC ERROR: #12 KSPFGMRESCycle() at /home/hhornik/Software/PETSc/src/ksp/ksp/impls/gmres/fgmres/fgmres.c:123
[0]PETSC ERROR: #13 KSPSolve_FGMRES() at /home/hhornik/Software/PETSc/src/ksp/ksp/impls/gmres/fgmres/fgmres.c:235
[0]PETSC ERROR: #14 KSPSolve_Private() at /home/hhornik/Software/PETSc/src/ksp/ksp/interface/itfunc.c:906
[0]PETSC ERROR: #15 KSPSolve() at /home/hhornik/Software/PETSc/src/ksp/ksp/interface/itfunc.c:1079
[0]PETSC ERROR: #16 applySolver() at /home/hhornik/gismo/optional/gsIncompressibleFlow/src/gsINSSolver.hpp:531

I could not find any solution for this so far. My question is: Is it possible to use the LSC preconditioner in such case, where the matrix blocks are of type MATNEST? And if so, how?
Thank you,
Hana Honnerova

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