[petsc-users] Solving Poisson equation with multigrid

[Michele Rosso]

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:

#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 
> <mailto: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>  <mailto: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

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20130529/03de632a/attachment.html>