[petsc-users] Method and PC for indefinite FE-problem

[Matthew Knepley]

On Wed, May 9, 2012 at 12:14 PM, Mårten Ullberg <martenullberg at gmail.com>wrote:

> Dear all,
>
> I am currently working on some large soil-structure interaction
> problems and therefor I have a finite element discretization that is
> going be solved in the frequency domain. This results in a symmetric,
> but indefinite matrix. I have not been able to find a proper method to
> use when solving it with PETSc.
>
> I was wondering if you guys have any recommendation on what to try,
> both concerning method but especially the PC? Is it recommended to use
> a composite PC for indefinite problems? I have tried the methods (such
> as MINRES, SYMMLQ) that are suggested for indefinite problems with no
> success. For small problems, GMRES+ASM+LU works fine, but for larger
> the memory consumption goes off the chart. I've also been able to use
> MUMPS but find it both memory and time consuming.
>
> I apologize for my lack of knowledge about iterative methods,
>

It sounds like you are trying to solve the Helmholtz equation. No one knows
how to do this with iterative methods. Sorry the answer is so pessimistic,
but
this is the truth unfortunately. If you can find a method you think will
work, we
can tell you how to do it in PETSc.

    Matt


> Best regards,
> Mårten

-- 
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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