[petsc-users] gamg failure with petsc-dev

[Stephan Kramer]

On 21/03/14 04:24, Jed Brown wrote:
> Stephan Kramer <s.kramer at imperial.ac.uk> writes:
>
>> We have been having some problems with GAMG on petsc-dev (master) for
>> cases that worked fine on petsc 3.4. We're solving a Stokes equation
>> (just the velocity block) for a simple convection in a square box
>> (isoviscous). The problem only occurs if we supply a near null space
>> (via MatSetNearNullSpace) where we supply the usual (1,0) (0,1) and
>> (-y,x) (near) null space vectors. If we supply those, the smoother
>> complains that the diagonal of the A matrix at the first coarsened
>> level contains a zero. If I dump out the prolongator from the finest
>> to the first coarsened level it indeed contains a zero column at that
>> same index. We're pretty confident that the fine level A matrix is
>> correct (it solves fine with LU). I've briefly spoken to Matt about
>> this and he suggested trying to run with -pc_gamg_agg_nsmooths 0 (as
>> the default changed from 3.4 -> dev) but that didn't make any
>> difference, the dumped out prolongator still has zero columns, and it
>> crashes in the same way. Do you have any further suggestions what to
>> try and how to further debug this?
>
> Do you set the block size?  Can you reproduce by modifying
> src/ksp/ksp/examples/tutorials/ex49.c (plane strain elasticity)?
>

I don't set a block size, no. About ex49: Ah great, with master (just updated now) I get:

[skramer at stommel]{/data/stephan/git/petsc/src/ksp/ksp/examples/tutorials}$ ./ex49 -elas_pc_type gamg -mx 100 -my 100 -mat_no_inode
[0]PETSC ERROR: --------------------- Error Message --------------------------------------------------------------
[0]PETSC ERROR: Arguments are incompatible
[0]PETSC ERROR: Zero diagonal on row 1
[0]PETSC ERROR: See http://http://www.mcs.anl.gov/petsc/documentation/faq.html for trouble shooting.
[0]PETSC ERROR: Petsc Development GIT revision: v3.4.4-3671-gbb161d1  GIT Date: 2014-03-21 01:14:15 +0000
[0]PETSC ERROR: ./ex49 on a linux-gnu-c-opt named stommel by skramer Fri Mar 21 11:25:55 2014
[0]PETSC ERROR: Configure options --download-fblaslapack=1 --download-blacs=1 --download-scalapack=1 --download-ptscotch=1 --download-mumps=1 --download-hypre=1 --download-suitesparse=1 --download-ml=1
[0]PETSC ERROR: #1 MatInvertDiagonal_SeqAIJ() line 1728 in /data/stephan/git/petsc/src/mat/impls/aij/seq/aij.c
[0]PETSC ERROR: #2 MatSOR_SeqAIJ() line 1760 in /data/stephan/git/petsc/src/mat/impls/aij/seq/aij.c
[0]PETSC ERROR: #3 MatSOR() line 3734 in /data/stephan/git/petsc/src/mat/interface/matrix.c
[0]PETSC ERROR: #4 PCApply_SOR() line 35 in /data/stephan/git/petsc/src/ksp/pc/impls/sor/sor.c
[0]PETSC ERROR: #5 PCApply() line 440 in /data/stephan/git/petsc/src/ksp/pc/interface/precon.c
[0]PETSC ERROR: #6 KSP_PCApply() line 227 in /data/stephan/git/petsc/include/petsc-private/kspimpl.h
[0]PETSC ERROR: #7 KSPSolve_Chebyshev() line 456 in /data/stephan/git/petsc/src/ksp/ksp/impls/cheby/cheby.c
[0]PETSC ERROR: #8 KSPSolve() line 458 in /data/stephan/git/petsc/src/ksp/ksp/interface/itfunc.c
[0]PETSC ERROR: #9 PCMGMCycle_Private() line 19 in /data/stephan/git/petsc/src/ksp/pc/impls/mg/mg.c
[0]PETSC ERROR: #10 PCMGMCycle_Private() line 48 in /data/stephan/git/petsc/src/ksp/pc/impls/mg/mg.c
[0]PETSC ERROR: #11 PCApply_MG() line 330 in /data/stephan/git/petsc/src/ksp/pc/impls/mg/mg.c
[0]PETSC ERROR: #12 PCApply() line 440 in /data/stephan/git/petsc/src/ksp/pc/interface/precon.c
[0]PETSC ERROR: #13 KSP_PCApply() line 227 in /data/stephan/git/petsc/include/petsc-private/kspimpl.h
[0]PETSC ERROR: #14 KSPInitialResidual() line 63 in /data/stephan/git/petsc/src/ksp/ksp/interface/itres.c
[0]PETSC ERROR: #15 KSPSolve_GMRES() line 234 in /data/stephan/git/petsc/src/ksp/ksp/impls/gmres/gmres.c
[0]PETSC ERROR: #16 KSPSolve() line 458 in /data/stephan/git/petsc/src/ksp/ksp/interface/itfunc.c
[0]PETSC ERROR: #17 solve_elasticity_2d() line 1053 in /data/stephan/git/petsc/src/ksp/ksp/examples/tutorials/ex49.c
[0]PETSC ERROR: #18 main() line 1104 in /data/stephan/git/petsc/src/ksp/ksp/examples/tutorials/ex49.c
[0]PETSC ERROR: ----------------End of Error Message -------send entire error message to petsc-maint at mcs.anl.gov----------

Which is the same error we were getting on our problem
Cheers
Stephan