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<div class="moz-cite-prefix">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" ?<br>
<br>
Thomas<br>
<br>
Am 20.11.2012 08:19, schrieb Jed Brown:<br>
</div>
<blockquote
cite="mid:CAM9tzS=WJYD66KBM43L=uLG_s8R9N_BF42kNiD-ZBNVyLWbrPg@mail.gmail.com"
type="cite">-mg_coarse_pc_type svd
<div><br>
</div>
<div>(or configure any other coarse solver that works for singular
systems, including adding a shift or using an iterative method)<br>
<div class="gmail_extra"><br>
<br>
<div class="gmail_quote">
On Tue, Nov 20, 2012 at 7:56 AM, Thomas Witkowski <span
dir="ltr"><<a moz-do-not-send="true"
href="mailto:thomas.witkowski@tu-dresden.de"
target="_blank">thomas.witkowski@tu-dresden.de</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
When I try to use GAMG for solviing a singular system
(Laplace matrix with Neuman boundaries), it crashes with
the following error:<br>
<br>
[0]PETSC ERROR: --------------------- Error Message
------------------------------------<br>
[0]PETSC ERROR: Detected zero pivot in LU factorization:<br>
[0]PETSC ERROR: Zero pivot row 65 value 9.19403e-17
tolerance 2.22045e-14!<br>
[0]PETSC ERROR: MatPivotCheck_none() line 585 in
/lustre/jhome22/hdr06/hdr060/petsc/build/petsc-dev/include/petsc-private/matimpl.h<br>
[0]PETSC ERROR: MatPivotCheck() line 604 in
/lustre/jhome22/hdr06/hdr060/petsc/build/petsc-dev/include/petsc-private/matimpl.h<br>
[0]PETSC ERROR: MatLUFactorNumeric_SeqAIJ() line 570 in
/lustre/jhome22/hdr06/hdr060/petsc/build/petsc-dev/src/mat/impls/aij/seq/aijfact.c<br>
[0]PETSC ERROR: MatLUFactorNumeric() line 2862 in
/lustre/jhome22/hdr06/hdr060/petsc/build/petsc-dev/src/mat/interface/matrix.c<br>
[0]PETSC ERROR: PCSetUp_LU() line 160 in
/lustre/jhome22/hdr06/hdr060/petsc/build/petsc-dev/src/ksp/pc/impls/factor/lu/lu.c<br>
[0]PETSC ERROR: PCSetUp() line 832 in
/lustre/jhome22/hdr06/hdr060/petsc/build/petsc-dev/src/ksp/pc/interface/precon.c<br>
[0]PETSC ERROR: KSPSetUp() line 278 in
/lustre/jhome22/hdr06/hdr060/petsc/build/petsc-dev/src/ksp/ksp/interface/itfunc.c<br>
[0]PETSC ERROR: PCSetUpOnBlocks_BJacobi_Singleblock() line
719 in /lustre/jhome22/hdr06/hdr060/petsc/build/petsc-dev/src/ksp/pc/impls/bjacobi/bjacobi.c<br>
[0]PETSC ERROR: PCSetUpOnBlocks() line 865 in
/lustre/jhome22/hdr06/hdr060/petsc/build/petsc-dev/src/ksp/pc/interface/precon.c<br>
[0]PETSC ERROR: KSPSetUpOnBlocks() line 154 in
/lustre/jhome22/hdr06/hdr060/petsc/build/petsc-dev/src/ksp/ksp/interface/itfunc.c<br>
[0]PETSC ERROR: KSPSolve() line 403 in
/lustre/jhome22/hdr06/hdr060/petsc/build/petsc-dev/src/ksp/ksp/interface/itfunc.c<br>
[0]PETSC ERROR: PCMGMCycle_Private() line 20 in
/lustre/jhome22/hdr06/hdr060/petsc/build/petsc-dev/src/ksp/pc/impls/mg/mg.c<br>
[0]PETSC ERROR: PCMGMCycle_Private() line 49 in
/lustre/jhome22/hdr06/hdr060/petsc/build/petsc-dev/src/ksp/pc/impls/mg/mg.c<br>
[0]PETSC ERROR: PCMGMCycle_Private() line 49 in
/lustre/jhome22/hdr06/hdr060/petsc/build/petsc-dev/src/ksp/pc/impls/mg/mg.c<br>
[0]PETSC ERROR: PCMGMCycle_Private() line 49 in
/lustre/jhome22/hdr06/hdr060/petsc/build/petsc-dev/src/ksp/pc/impls/mg/mg.c<br>
[0]PETSC ERROR: PCApplyRichardson_MG() line 104 in
/lustre/jhome22/hdr06/hdr060/petsc/build/petsc-dev/src/ksp/pc/impls/mg/mg.c<br>
[0]PETSC ERROR: PCApplyRichardson() line 780 in
/lustre/jhome22/hdr06/hdr060/petsc/build/petsc-dev/src/ksp/pc/interface/precon.c<br>
[0]PETSC ERROR: KSPSolve_Richardson() line 69 in
/lustre/jhome22/hdr06/hdr060/petsc/build/petsc-dev/src/ksp/ksp/impls/rich/rich.c<br>
[0]PETSC ERROR: KSPSolve() line 446 in
/lustre/jhome22/hdr06/hdr060/petsc/build/petsc-dev/src/ksp/ksp/interface/itfunc.c<br>
<br>
How to fix this problem? I already checked the gamg
options, but I have not found something what could be
related to this problem.<span class="HOEnZb"><font
color="#888888"><br>
<br>
Thomas<br>
</font></span></blockquote>
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