Isa, BJacobi LU or ilu can develop zero pivots as you decrease the diagonal block size. You can force it to become positive definite with the runtime option '-sub_pc_factor_shift_positive_definit' or without zero pivots with '-sub_pc_factor_shift_nonzero.' (or -pc_factor_shift_positive_definit/-pc_factor_shift_nonzero for ilu). This might decrease the effectiveness of the preconditioner though.
Hong On Thu, 21 Dec 2006, Isabel Gil wrote: > Hello PETSc's users, > > I have just started to use PETSc and when I try to solve the matricial > system I obtain the following error sentences: > > [0]PETSC ERROR: MatLUFactorNumeric_SeqAIJ() line 538 in > src/mat/impls/aij/seq/aijfact.c > [0]PETSC ERROR: Detected zero pivot in LU factorization > see > http://www.mcs.anl.gov/petsc/petsc-2/documentation/troubleshooting.html#ZeroPivot! > [0]PETSC ERROR: Zero pivot row 277017 value 2.16144e-10 tolerance 1e-12 > * rs 526.244! > [0]PETSC ERROR: MatLUFactorNumeric() line 1843 in src/mat/interface/matrix.c > [0]PETSC ERROR: PCSetUp_ILU() line 854 in src/ksp/pc/impls/ilu/ilu.c > [0]PETSC ERROR: PCSetUp() line 797 in src/ksp/pc/interface/precon.c > [0]PETSC ERROR: KSPSetUp() line 232 in src/ksp/ksp/interface/itfunc.c > [0]PETSC ERROR: PCSetUpOnBlocks_BJacobi_Singleblock() line 747 in > src/ksp/pc/impls/bjacobi/bjacobi.c > [0]PETSC ERROR: PCSetUpOnBlocks() line 830 in src/ksp/pc/interface/precon.c > [0]PETSC ERROR: KSPSetUpOnBlocks() line 156 in > src/ksp/ksp/interface/itfunc.c > [0]PETSC ERROR: KSPSolve() line 344 in src/ksp/ksp/interface/itfunc.c > > I would be really grateful if you could say to me where the problem > could be in order to sort it out. > > Thanks in advance and best regards > Isa > >
