[petsc-users] PCFIELDSPLIT with BoomerAMG preconditioning on a Schur Complement

[Matthew Knepley]

On Tue, Apr 20, 2021 at 4:33 PM Jorti, Zakariae via petsc-users <
petsc-users at mcs.anl.gov> wrote:

> Hello,
>
>
> I have a block matrix A,
>
>
> [A_{00}   A_{01}]
>
> [A_{10}   A_{11}] ,
>
>
> and am trying to use PCFIELDSPLIT as a preconditioner on it. The
> preconditioner has this shape:
>
>
> [inv(A_{00})       0     ]
>
> [  0                -ksp(S)] ;
>
>
> where S is the Schur Complement matrix:
>
> S = A_{11} - A_{10} * inv(A_{00}) * A_{01},
>
> that I get by calling:
>
>
> MatGetSchurComplement(A, isrow0, iscol0, isrow1, iscol1, MAT_INITIAL_MATRIX, &S, MAT_SCHUR_COMPLEMENT_AINV_DIAG,
> MAT_IGNORE_MATRIX, NULL);
>
> I would like to set BoomerAMG preconditioner for ksp(S). So, I am calling:
>
>
>
> PCFieldSplitGetSubKSP(pc, &n, &subksp);
>
> KSPSetOperators(subksp[1], S, S);
>
> KSPGetPC(subksp[1], subpc);
>
> PCSetType(subpc,"boomeramg");
>
>
> but I end up getting the following error:
>
>
> [0]PETSC ERROR: No support for this operation for this object type
>
> [0]PETSC ERROR: Mat type schurcomplement
>
> [0]PETSC ERROR: See https://www.mcs.anl.gov/petsc/documentation/faq.html
> for trouble shooting.
>
> [0]PETSC ERROR: Petsc Release Version 3.14.2, Dec 03, 2020
>
> [0]PETSC ERROR: ./mimeticcurleuler2 on a arch-linux-c-debug named nid00140
> by zjorti Tue Apr 20 12:23:34 2021
>
> [0]PETSC ERROR: Configure options CC=cc CXX=CC FC=ftn COPTFLAGS=-g
> CXXOPTFLAGS=-g FOPTFLAGS=-g --download-hypre --with-debugging=1
> --with-cxx-dialect=C++11
>
> [0]PETSC ERROR: #1 MatGetRow() line 561 in
> /global/u1/z/zjorti/Software/petsc-3.14.2/src/mat/interface/matrix.c
>
> [0]PETSC ERROR: #2 MatConvert_Basic() line 53 in
> /global/u1/z/zjorti/Software/petsc-3.14.2/src/mat/utils/convert.c
>
> [0]PETSC ERROR: #3 MatConvert() line 4254 in
> /global/u1/z/zjorti/Software/petsc-3.14.2/src/mat/interface/matrix.c
>
> [0]PETSC ERROR: #4 PCSetUp_HYPRE() line 231 in
> /global/u1/z/zjorti/Software/petsc-3.14.2/src/ksp/pc/impls/hypre/hypre.c
>
> [0]PETSC ERROR: #5 PCSetUp() line 1009 in
> /global/u1/z/zjorti/Software/petsc-3.14.2/src/ksp/pc/interface/precon.c
>
> [0]PETSC ERROR: #6 KSPSetUp() line 406 in
> /global/u1/z/zjorti/Software/petsc-3.14.2/src/ksp/ksp/interface/itfunc.c
>
> [0]PETSC ERROR: #7 KSPSolve_Private() line 658 in
> /global/u1/z/zjorti/Software/petsc-3.14.2/src/ksp/ksp/interface/itfunc.c
>
> [0]PETSC ERROR: #8 KSPSolve() line 889 in
> /global/u1/z/zjorti/Software/petsc-3.14.2/src/ksp/ksp/interface/itfunc.c
>
> [0]PETSC ERROR: #9 PCApply_FieldSplit_Schur() line 1133 in
> /global/u1/z/zjorti/Software/petsc-3.14.2/src/ksp/pc/impls/fieldsplit/fieldsplit.c
>
> [0]PETSC ERROR: #10 PCApply() line 444 in
> /global/u1/z/zjorti/Software/petsc-3.14.2/src/ksp/pc/interface/precon.c
>
> [0]PETSC ERROR: #11 KSP_PCApply() line 283 in
> /global/u1/z/zjorti/Software/petsc-3.14.2/include/petsc/private/kspimpl.h
>
> [0]PETSC ERROR: #12 KSPInitialResidual() line 65 in
> /global/u1/z/zjorti/Software/petsc-3.14.2/src/ksp/ksp/interface/itres.c
>
> [0]PETSC ERROR: #13 KSPSolve_GMRES() line 245 in
> /global/u1/z/zjorti/Software/petsc-3.14.2/src/ksp/ksp/impls/gmres/gmres.c
>
> [0]PETSC ERROR: #14 KSPSolve_Private() line 719 in
> /global/u1/z/zjorti/Software/petsc-3.14.2/src/ksp/ksp/interface/itfunc.c
>
> [0]PETSC ERROR: #15 KSPSolve() line 889 in
> /global/u1/z/zjorti/Software/petsc-3.14.2/src/ksp/ksp/interface/itfunc.c
>
> [0]PETSC ERROR: #16 SNESSolve_KSPONLY() line 51 in
> /global/u1/z/zjorti/Software/petsc-3.14.2/src/snes/impls/ksponly/ksponly.c
>
> [0]PETSC ERROR: #17 SNESSolve() line 4569 in
> /global/u1/z/zjorti/Software/petsc-3.14.2/src/snes/interface/snes.c
>
> [0]PETSC ERROR: #18 TSTheta_SNESSolve() line 185 in
> /global/u1/z/zjorti/Software/petsc-3.14.2/src/ts/impls/implicit/theta/theta.c
>
> [0]PETSC ERROR: #19 TSStep_Theta() line 223 in
> /global/u1/z/zjorti/Software/petsc-3.14.2/src/ts/impls/implicit/theta/theta.c
>
> [0]PETSC ERROR: #20 TSStep() line 3757 in
> /global/u1/z/zjorti/Software/petsc-3.14.2/src/ts/interface/ts.c
>
> [0]PETSC ERROR: #21 TSSolve() line 4154 in
> /global/u1/z/zjorti/Software/petsc-3.14.2/src/ts/interface/ts.c
>
>
> Am I doing something wrong here? How can I fix this?
>
It really is best to do this with options. It will take a lot of
programming to replicate what you can do.

You are trying to precondition an implicit matrix (S) with Boomeramg, which
needs explicit entries. You can tell PCFIELDSPLIT to build an
explicit matrix for the Schur complement:


https://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/PC/PCFieldSplitSetSchurPre.html

  Thanks,

     Matt

> Many thanks.
>
>
> Best regards,
>
>
> Zakariae Jorti
>
>
>
>


-- 
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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