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

[Pierre Jolivet]

> 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

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20240211/e76f9fd0/attachment.html>