Some error when I try to solve a matricial system

[Hong Zhang]

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
>
>