[petsc-users] Using GAMG for solving singular systems

[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> 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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