Hello all, I am trying to use ML to solve a Poisson equation with Neumann BC (singular matrix) and found the thread below to avoid a zero pivot error. I used the option that Barry suggests, -mg_coarse_pc_factor_shift_type nonzero, which works, but only when I run on a single processor. For two or more processors I still get a zero pivot error. Are there more options to be set for the parallel case?
Benjamin [1]PETSC ERROR: --------------------- Error Message ------------------------------------ [1]PETSC ERROR: Detected zero pivot in LU factorization: see http://www.mcs.anl.gov/petsc/documentation/faq.html#ZeroPivot! [1]PETSC ERROR: Zero pivot row 1 value 5.7431e-18 tolerance 2.22045e-14! [1]PETSC ERROR: ------------------------------------------------------------------------ [1]PETSC ERROR: Petsc Release Version 3.3.0, Patch 1, Fri Jun 15 09:30:49 CDT 2012 [1]PETSC ERROR: See docs/changes/index.html for recent updates. [1]PETSC ERROR: [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 1 value 5.7431e-18 tolerance 2.22045e-14! [0]PETSC ERROR: ------------------------------------------------------------------------ [0]PETSC ERROR: Petsc Release Version 3.3.0, Patch 1, Fri Jun 15 09:30:49 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: bin/navier-stokes on a linux-gnu named gb-r3n32.irc.sara.nl by sanderse Tue Jul 17 10:04:05 2012 [0]PETSC ERROR: Libraries linked from /home/sanderse/Software/petsc-3.3-p1/linux-gnu-c-debug/lib [0]PETSC ERROR: Configure run at Mon Jul 16 21:06:33 2012 [0]PETSC ERROR: Configure options --with-cc=mpicc --with-fc=mpif90 --with-cxx=mpicxx --with-shared-libraries --with-hypre --download-hypre --with-blas-lapack-dir=/sara /sw/intel/Compiler/11.0/069 --with-hdf5 --download-hdf5 --with-debugging=0 --download-ml [0]PETSC ERROR: ------------------------------------------------------------------------ [0]PETSC ERROR: MatPivotCheck_none() line 583 in /home/sanderse/Software/petsc-3.3-p1/include/petsc-private/matimpl.h [0]PETSC ERROR: MatPivotCheck() line 602 in /home/sanderse/Software/petsc-3.3-p1/include/petsc-private/matimpl.h [0]PETSC ERROR: See docs/faq.html for hints about trouble shooting. [1]PETSC ERROR: See docs/index.html for manual pages. [1]PETSC ERROR: ------------------------------------------------------------------------ [1]PETSC ERROR: bin/navier-stokes on a linux-gnu named gb-r3n32.irc.sara.nl by sanderse Tue Jul 17 10:04:05 2012 [1]PETSC ERROR: Libraries linked from /home/sanderse/Software/petsc-3.3-p1/linux-gnu-c-debug/lib [1]PETSC ERROR: Configure run at Mon Jul 16 21:06:33 2012 [1]PETSC ERROR: Configure options --with-cc=mpicc --with-fc=mpif90 --with-cxx=mpicxx --with-shared-libraries --with-hypre --download-hypre --with-blas-lapack-dir=/sara /sw/intel/Compiler/11.0/069 --with-hdf5 --download-hdf5 --with-debugging=0 --download-ml [1]PETSC ERROR: ------------------------------------------------------------------------ [1]PETSC ERROR: MatPivotCheck_none() line 583 in /home/sanderse/Software/petsc-3.3-p1/include/petsc-private/matimpl.h MatLUFactorNumeric_SeqAIJ_Inode() line 1469 in /home/sanderse/Software/petsc-3.3-p1/src/mat/impls/aij/seq/inode.c [0]PETSC ERROR: MatLUFactorNumeric() line 2790 in /home/sanderse/Software/petsc-3.3-p1/src/mat/interface/matrix.c [0]PETSC ERROR: PCSetUp_LU() line 160 in /home/sanderse/Software/petsc-3.3-p1/src/ksp/pc/impls/factor/lu/lu.c [0]PETSC ERROR: PCSetUp() line 832 in /home/sanderse/Software/petsc-3.3-p1/src/ksp/pc/interface/precon.c [0]PETSC ERROR: KSPSetUp() line 278 in /home/sanderse/Software/petsc-3.3-p1/src/ksp/ksp/interface/itfunc.c [0]PETSC ERROR: PCSetUp_Redundant() line 176 in /home/sanderse/Software/petsc-3.3-p1/src/ksp/pc/impls/redundant/redundant.c [0]PETSC ERROR: PCSetUp() line 832 in /home/sanderse/Software/petsc-3.3-p1/src/ksp/pc/interface/precon.c [0]PETSC ERROR: KSPSetUp() line 278 in /home/sanderse/Software/petsc-3.3-p1/src/ksp/ksp/interface/itfunc.c [0]PETSC ERROR: PCSetUp_MG() line 729 in /home/sanderse/Software/petsc-3.3-p1/src/ksp/pc/impls/mg/mg.c [0]PETSC ERROR: [1]PETSC ERROR: MatPivotCheck() line 602 in /home/sanderse/Software/petsc-3.3-p1/include/petsc-private/matimpl.h [1]PETSC ERROR: MatLUFactorNumeric_SeqAIJ_Inode() line 1469 in /home/sanderse/Software/petsc-3.3-p1/src/mat/impls/aij/seq/inode.c [1]PETSC ERROR: MatLUFactorNumeric() line 2790 in /home/sanderse/Software/petsc-3.3-p1/src/mat/interface/matrix.c [1]PETSC ERROR: PCSetUp_LU() line 160 in /home/sanderse/Software/petsc-3.3-p1/src/ksp/pc/impls/factor/lu/lu.c [1]PETSC ERROR: PCSetUp_ML() line 820 in /home/sanderse/Software/petsc-3.3-p1/src/ksp/pc/impls/ml/ml.c [0]PETSC ERROR: PCSetUp() line 832 in /home/sanderse/Software/petsc-3.3-p1/src/ksp/pc/interface/precon.c [0]PETSC ERROR: KSPSetUp() line 278 in /home/sanderse/Software/petsc-3.3-p1/src/ksp/ksp/interface/itfunc.c PCSetUp() line 832 in /home/sanderse/Software/petsc-3.3-p1/src/ksp/pc/interface/precon.c [1]PETSC ERROR: KSPSetUp() line 278 in /home/sanderse/Software/petsc-3.3-p1/src/ksp/ksp/interface/itfunc.c [1]PETSC ERROR: PCSetUp_Redundant() line 176 in /home/sanderse/Software/petsc-3.3-p1/src/ksp/pc/impls/redundant/redundant.c [1]PETSC ERROR: PCSetUp() line 832 in /home/sanderse/Software/petsc-3.3-p1/src/ksp/pc/interface/precon.c [1]PETSC ERROR: KSPSetUp() line 278 in /home/sanderse/Software/petsc-3.3-p1/src/ksp/ksp/interface/itfunc.c [1]PETSC ERROR: PCSetUp_MG() line 729 in /home/sanderse/Software/petsc-3.3-p1/src/ksp/pc/impls/mg/mg.c [1]PETSC ERROR: PCSetUp_ML() line 820 in /home/sanderse/Software/petsc-3.3-p1/src/ksp/pc/impls/ml/ml.c [1]PETSC ERROR: PCSetUp() line 832 in /home/sanderse/Software/petsc-3.3-p1/src/ksp/pc/interface/precon.c [1]PETSC ERROR: KSPSetUp() line 278 in /home/sanderse/Software/petsc-3.3-p1/src/ksp/ksp/interface/itfunc.c Op 3 jun 2011, om 14:26 heeft Barry Smith het volgende geschreven: > > It is the direct solver on the the coarse grid that is finding the zero > pivot (since the coarse grid problem like all the levels has a null space). > > You can use the option -mg_coarse_pc_factor_shift_type nonzero (in > petsc-3.1 or petsc-dev) Also keep the KSPSetNullSpace() function you are > using. > > > Barry > > On Jun 3, 2011, at 3:54 AM, Stijn A. M. Vantieghem wrote: > >> Dear all, >> >> I am using PETSc (Fortran interface) to solve a Poisson equation with >> Neumann boundary conditions. Up till now, I managed to do this with Hypre's >> BoomerAMG. Now, I am investigating whether I can improve the performance of >> my code by using ML. However, at execution I receive a zero pivot error; I >> tried to remove the (constant) null space with KSPSetNullSpace, but this >> didn't solve my problem. Do you have an idea of what I'm doing wrong? >> Thanks. >> >> The relevant portions of my code are as follows: >> >> !**************************************************** >> call KSPCreate(PETSC_COMM_WORLD,ksp,ierr) >> call KSPSetOperators(ksp,M,M,DIFFERENT_NONZERO_PATTERN,ierr) >> >> call MatNullSpaceCreate(PETSC_COMM_WORLD,PETSC_TRUE,0,PETSC_NULL,sp,ierr) >> call KSPSetNullSpace(ksp,sp,ierr) >> >> call KSPGetPC(ksp,pc,ierr) >> call PCSetType(pc,PCML,ierr) >> >> call KSPSetFromOptions(ksp,ierr) >> ... >> call KSPSetInitialGuessNonzero(ksp,PETSC_TRUE,ierr) >> call KSPSolve(ksp,petsc_rhs,petsc_pressure,ierr) >> !**************************************************** >> >> and the error message is: >> >> [0]PETSC ERROR: --------------------- Error Message >> ------------------------------------ >> [0]PETSC ERROR: Detected zero pivot in LU factorization >> see >> http://www.mcs.anl.gov/petsc/petsc-as/documentation/troubleshooting.html#ZeroPivot! >> [0]PETSC ERROR: Zero pivot row 0 value 3.57045e-20 tolerance 1e-12! >> [0]PETSC ERROR: >> ------------------------------------------------------------------------ >> ... >> [0]PETSC ERROR: >> ------------------------------------------------------------------------ >> [0]PETSC ERROR: MatLUFactorNumeric_SeqAIJ() line 574 in >> src/mat/impls/aij/seq/aijfact.c >> [0]PETSC ERROR: MatLUFactorNumeric() line 2587 in src/mat/interface/matrix.c >> [0]PETSC ERROR: PCSetUp_LU() line 158 in src/ksp/pc/impls/factor/lu/lu.c >> [0]PETSC ERROR: PCSetUp() line 795 in src/ksp/pc/interface/precon.c >> [0]PETSC ERROR: KSPSetUp() line 237 in src/ksp/ksp/interface/itfunc.c >> [0]PETSC ERROR: PCSetUp_MG() line 602 in src/ksp/pc/impls/mg/mg.c >> [0]PETSC ERROR: PCSetUp_ML() line 668 in src/ksp/pc/impls/ml/ml.c >> [0]PETSC ERROR: PCSetUp() line 795 in src/ksp/pc/interface/precon.c >> [0]PETSC ERROR: KSPSetUp() line 237 in src/ksp/ksp/interface/itfunc.c >> [0]PETSC ERROR: KSPSolve() line 353 in src/ksp/ksp/interface/itfunc.c >> >> Regards >> Stijn >> >> Stijn A.M. Vantieghem >> Earth and Planetary Magnetism >> Institute for Geophysics >> ETH Z?rich >> Sonneggstrasse 5 - CH 8092 Z?rich >> tel: +41 44 632 39 90 >> e-mail: stijn.vantieghem at erdw.ethz.ch >> >> >> >> >
