Yes, as usual. Run with -help to see all options.<div class="gmail_extra"><br><br><div class="gmail_quote">On Tue, Nov 20, 2012 at 8:22 AM, Thomas Witkowski <span dir="ltr"><<a 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">
  
    
  
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    <div>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><div><div class="h5">
    <blockquote type="cite">-mg_coarse_pc_type svd
      <div><br>
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      <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 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><font color="#888888"><br>
                  <br>
                  Thomas<br>
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