[petsc-users] Using GAMG for solving singular systems

[Thomas Witkowski]

Okay, I found it in the parameter list from -help!


Am 20.11.2012 08:22, schrieb Thomas Witkowski:
> Which prefix must be added here? When I use "-laplace_pc_type gamg", 
> must this parameter be set with "-laplace_mg_coarse_pc_type svd" ?
>
> Thomas
>
> Am 20.11.2012 08:19, schrieb Jed Brown:
>> -mg_coarse_pc_type svd
>>
>> (or configure any other coarse solver that works for singular 
>> systems, including adding a shift or using an iterative method)
>>
>>
>> On Tue, Nov 20, 2012 at 7:56 AM, Thomas Witkowski 
>> <thomas.witkowski at tu-dresden.de 
>> <mailto:thomas.witkowski at tu-dresden.de>> wrote:
>>
>>     When I try to use GAMG for solviing a singular system (Laplace
>>     matrix with Neuman boundaries), it crashes with the following error:
>>
>>     [0]PETSC ERROR: --------------------- Error Message
>>     ------------------------------------
>>     [0]PETSC ERROR: Detected zero pivot in LU factorization:
>>     [0]PETSC ERROR: Zero pivot row 65 value 9.19403e-17 tolerance
>>     2.22045e-14!
>>     [0]PETSC ERROR: MatPivotCheck_none() line 585 in
>>     /lustre/jhome22/hdr06/hdr060/petsc/build/petsc-dev/include/petsc-private/matimpl.h
>>     [0]PETSC ERROR: MatPivotCheck() line 604 in
>>     /lustre/jhome22/hdr06/hdr060/petsc/build/petsc-dev/include/petsc-private/matimpl.h
>>     [0]PETSC ERROR: MatLUFactorNumeric_SeqAIJ() line 570 in
>>     /lustre/jhome22/hdr06/hdr060/petsc/build/petsc-dev/src/mat/impls/aij/seq/aijfact.c
>>     [0]PETSC ERROR: MatLUFactorNumeric() line 2862 in
>>     /lustre/jhome22/hdr06/hdr060/petsc/build/petsc-dev/src/mat/interface/matrix.c
>>     [0]PETSC ERROR: PCSetUp_LU() line 160 in
>>     /lustre/jhome22/hdr06/hdr060/petsc/build/petsc-dev/src/ksp/pc/impls/factor/lu/lu.c
>>     [0]PETSC ERROR: PCSetUp() line 832 in
>>     /lustre/jhome22/hdr06/hdr060/petsc/build/petsc-dev/src/ksp/pc/interface/precon.c
>>     [0]PETSC ERROR: KSPSetUp() line 278 in
>>     /lustre/jhome22/hdr06/hdr060/petsc/build/petsc-dev/src/ksp/ksp/interface/itfunc.c
>>     [0]PETSC ERROR: PCSetUpOnBlocks_BJacobi_Singleblock() line 719 in
>>     /lustre/jhome22/hdr06/hdr060/petsc/build/petsc-dev/src/ksp/pc/impls/bjacobi/bjacobi.c
>>     [0]PETSC ERROR: PCSetUpOnBlocks() line 865 in
>>     /lustre/jhome22/hdr06/hdr060/petsc/build/petsc-dev/src/ksp/pc/interface/precon.c
>>     [0]PETSC ERROR: KSPSetUpOnBlocks() line 154 in
>>     /lustre/jhome22/hdr06/hdr060/petsc/build/petsc-dev/src/ksp/ksp/interface/itfunc.c
>>     [0]PETSC ERROR: KSPSolve() line 403 in
>>     /lustre/jhome22/hdr06/hdr060/petsc/build/petsc-dev/src/ksp/ksp/interface/itfunc.c
>>     [0]PETSC ERROR: PCMGMCycle_Private() line 20 in
>>     /lustre/jhome22/hdr06/hdr060/petsc/build/petsc-dev/src/ksp/pc/impls/mg/mg.c
>>     [0]PETSC ERROR: PCMGMCycle_Private() line 49 in
>>     /lustre/jhome22/hdr06/hdr060/petsc/build/petsc-dev/src/ksp/pc/impls/mg/mg.c
>>     [0]PETSC ERROR: PCMGMCycle_Private() line 49 in
>>     /lustre/jhome22/hdr06/hdr060/petsc/build/petsc-dev/src/ksp/pc/impls/mg/mg.c
>>     [0]PETSC ERROR: PCMGMCycle_Private() line 49 in
>>     /lustre/jhome22/hdr06/hdr060/petsc/build/petsc-dev/src/ksp/pc/impls/mg/mg.c
>>     [0]PETSC ERROR: PCApplyRichardson_MG() line 104 in
>>     /lustre/jhome22/hdr06/hdr060/petsc/build/petsc-dev/src/ksp/pc/impls/mg/mg.c
>>     [0]PETSC ERROR: PCApplyRichardson() line 780 in
>>     /lustre/jhome22/hdr06/hdr060/petsc/build/petsc-dev/src/ksp/pc/interface/precon.c
>>     [0]PETSC ERROR: KSPSolve_Richardson() line 69 in
>>     /lustre/jhome22/hdr06/hdr060/petsc/build/petsc-dev/src/ksp/ksp/impls/rich/rich.c
>>     [0]PETSC ERROR: KSPSolve() line 446 in
>>     /lustre/jhome22/hdr06/hdr060/petsc/build/petsc-dev/src/ksp/ksp/interface/itfunc.c
>>
>>     How to fix this problem? I already checked the gamg options, but
>>     I have not found something what could be related to this problem.
>>
>>     Thomas
>>
>>
>

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