[petsc-users] Is PCFactorSetZeroPivot() effective?

[Matthew Knepley]

On Wed, May 30, 2012 at 7:20 PM, Jozsef Bakosi <jbakosi at lanl.gov> wrote:

> Hello,
>
> I have a mesh with very small cell sizes and in a Poisson equation CG solve
> with ML preconditioner I get the following error:
>
> [31]PETSC ERROR: --------------------- Error Message
> ------------------------------------
> [31]PETSC ERROR: Detected zero pivot in LU factorization see
>
> http://www.mcs.anl.gov/petsc/petsc-as/documentation/troubleshooting.html#ZeroPivot
> !
> [31]PETSC ERROR: Zero pivot row 537 value 9.41111e-13 tolerance 1e-12!
>
> I really would like PETSc to NOT treat matrix values lower than 1e-12 to
> be zero, so I'm trying to set the zero pivot to a lower value with
> PCFactorSetZeroPivot(), but I still get the same error message: as if
> the function call would have no effect. I also tried setting the
> zeropivot via PetscOptionsSetValue("-pc_factor_zeropivot", ...), but
> still no luck.
>
> Is there another way to set the zero pivot that I'm not aware of?
>

1) Always look at -ksp_view

2) I bet this is a subsolve, so that it would be -sub_pc_factor_zeropivot
<value>. You
    can verify by looking at -ksp_view


> Is there a way to query the zero pivot value?
>

3) Its printed out, 1.0e-12

   Matt


> Thanks,
> J
> --
> Jozsef Bakosi
> Computational Physics Group (CCS-2)
> MS T006, Los Alamos National Laboratory
> Los Alamos, NM 87545, USA
> email: jbakosi at lanl.gov
> work: 505-663-5607
> fax : 505-663-5504
>



-- 
What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to which their
experiments lead.
-- Norbert Wiener
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