[petsc-users] Solving Poisson equation with multigrid

[Matthew Knepley]

On Fri, May 24, 2013 at 5:18 PM, Michele Rosso <mrosso at uci.edu> wrote:

>  Using
>
> -pc_type gamg -pc_mg_cycle_type v -pc_gamg_agg_nsmooths 1
> -mg_coarse_sub_pc_factor_shift_type NONZERO  -option_left -ksp_view
>

This is what debugging is about. We are not running your problem. How could
this be debugged?

1) Run the problem w/o a null space so that it finishes

2) Look at the output for -ksp_view

3) Does the coarse solver say that it is shifted?

4) Are there options which were unused?

   Matt


> still produces the same error:
>
> [0]PCSetData_AGG bs=1 MM=131072
> [0]PETSC ERROR: --------------------- Error Message
> ------------------------------------
> [0]PETSC ERROR: Detected zero pivot in LU factorization:
> see http://www.mcs.anl.gov/petsc/documentation/faq.html#ZeroPivot!
> [0]PETSC ERROR: Zero pivot row 280 value 6.56964e-17 tolerance 2.22045e-14!
> [0]PETSC ERROR:
> ------------------------------------------------------------------------
> [0]PETSC ERROR: Petsc Release Version 3.3.0, Patch 3, Wed Aug 29 11:26:24
> CDT 2012
> [0]PETSC ERROR: See docs/changes/index.html for recent updates.
> [0]PETSC ERROR: See docs/faq.html for hints about trouble shooting.
> [0]PETSC ERROR: See docs/index.html for manual pages.
> [0]PETSC ERROR:
> ------------------------------------------------------------------------
> [0]PETSC ERROR: ./hit on a  named nid15363 by Unknown Fri May 24 17:06:50
> 2013
> [0]PETSC ERROR: Libraries linked from
> [0]PETSC ERROR: Configure run at
> [0]PETSC ERROR: Configure options
> [0]PETSC ERROR:
> ------------------------------------------------------------------------
> [0]PETSC ERROR: MatPivotCheck_none() line 583 in
> src/mat/impls/aij/seq//ptmp/skelly/petsc/3.3.03/cray_interlagos_build/real/src/include/petsc-private/matimpl.h
> [0]PETSC ERROR: MatPivotCheck() line 602 in
> src/mat/impls/aij/seq//ptmp/skelly/petsc/3.3.03/cray_interlagos_build/real/src/include/petsc-private/matimpl.h
> [0]PETSC ERROR: MatLUFactorNumeric_SeqAIJ() line 585 in
> src/mat/impls/aij/seq/aijfact.c
> [0]PETSC ERROR: MatLUFactorNumeric() line 2803 in
> src/mat/interface/matrix.c
> [0]PETSC ERROR: PCSetUp_LU() line 160 in src/ksp/pc/impls/factor/lu/lu.c
> [0]PETSC ERROR: PCSetUp() line 832 in src/ksp/pc/interface/precon.c
> [0]PETSC ERROR: KSPSetUp() line 278 in src/ksp/ksp/interface/itfunc.c
> [0]PETSC ERROR: PCSetUpOnBlocks_BJacobi_Singleblock() line 715 in
> src/ksp/pc/impls/bjacobi/bjacobi.c
> [0]PETSC ERROR: PCSetUpOnBlocks() line 865 in src/ksp/pc/interface/precon.c
> [0]PETSC ERROR: KSPSetUpOnBlocks() line 154 in
> src/ksp/ksp/interface/itfunc.c
> [0]PETSC ERROR: KSPSolve() line 403 in src/ksp/ksp/interface/itfunc.c
> [0]PETSC ERROR: PCSetUpOnBlocks_BJacobi_Singleblock() line 715 in
> src/ksp/pc/impls/bjacobi/bjacobi.c
> [0]PETSC ERROR: PCSetUpOnBlocks() line 865 in src/ksp/pc/interface/precon.c
> [0]PETSC ERROR: KSPSetUpOnBlocks() line 154 in
> src/ksp/ksp/interface/itfunc.c
> [0]PETSC ERROR: KSPSolve() line 403 in src/ksp/ksp/interface/itfunc.c
> [0]PETSC ERROR: PCMGMCycle_Private() line 20 in src/ksp/pc/impls/mg/mg.c
> [0]PETSC ERROR: PCMGMCycle_Private() line 49 in src/ksp/pc/impls/mg/mg.c
> [0]PETSC ERROR: PCMGMCycle_Private() line 49 in src/ksp/pc/impls/mg/mg.c
> [0]PETSC ERROR: PCMGMCycle_Private() line 49 in src/ksp/pc/impls/mg/mg.c
> [0]PETSC ERROR: PCApply_MG() line 326 in src/ksp/pc/impls/mg/mg.c
> [0]PETSC ERROR: PCApply() line 384 in src/ksp/pc/interface/precon.c
> [0]PETSC ERROR: KSPSolve_CG() line 139 in src/ksp/ksp/impls/cg/cg.c
> [0]PETSC ERROR: KSPSolve() line 446 in src/ksp/ksp/interface/itfunc.c
>
>  On 05/24/2013 02:51 PM, Jed Brown wrote:
>
> Michele Rosso <mrosso at uci.edu> <mrosso at uci.edu> writes:
>
>
>      With petsc-3.4 (which you should upgrade to), use
>     -mg_coarse_sub_pc_factor_shift_type NONZERO
>
>  Actually, use this with petsc-3.3 also (and please upgrade to
> petsc-3.4).
>
> The option you were passing was not being used.
>
>
>
>


-- 
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
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