[petsc-users] Solving Poisson equation with multigrid

Wed May 29 16:29:45 CDT 2013

On Wed, May 29, 2013 at 5:25 PM, Michele Rosso <mrosso at uci.edu> wrote:

>  Hi,
>
> I proceeded as Matt suggested. I am running without nullspace (Dirichlet's
> BCs) with the following options:
>
> -pc_type gamg  -pc_mg_cycle_type v  -pc_gamg_agg_nsmooths 1
> -mg_coarse_sub_pc_factor_shift_type NONZERO -ksp_view -options_left
>
> The results are fine and the run finishes. The output of -ksp_view does
> not say anything about the coarse solver being shifted.
> In fact the option  -mg_coarse_sub_pc_factor_shift_type NONZERO is not
> used:
>

Please show us the COMPLETE output.

  Thanks,

     Matt

> #PETSc Option Table entries:
> -ksp_view
> -mg_coarse_sub_pc_factor_shift_type NONZERO
> -options_left
> -pc_gamg_agg_nsmooths 1
> -pc_mg_cycle_type v
> -pc_type gamg
> #End of PETSc Option Table entries
> There is one unused database option. It is:
> Option left: name:-mg_coarse_sub_pc_factor_shift_type value: NONZERO
>
> Michele
>
>
>  On 05/24/2013 03:20 PM, Matthew Knepley wrote:
>
> 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
>
>
>

-- 
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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