[petsc-users] Convergence of iterative linear solver

[Eduardo]

I am solving a FEM solid mechanics linear elasticity model, for now the
only problem is the mesh that has needle-shaped and very flat elements.
Have you any suggestion of preconditioner (and references).
Thanks,
Eduardo

On Tue, Jun 2, 2015 at 4:11 AM, Barry Smith <bsmith at mcs.anl.gov> wrote:

>
> > On Jun 1, 2015, at 4:06 PM, Eduardo <erocha.ssa at gmail.com> wrote:
> >
> > I am solving a linear system for which the preconditioned residual
> decreases, but the true residual increases (or have an erratic behavior).
> According to Petsc FAQ, this is due to a preconditioner that is singular or
> close to singular. What can I do in this case? I used GMRES with ILU
> preconditioner.
>                                               ^^^^^^^^^^^^^^^
> >
> > Incidentally, I tried to solve a smaller system with a direct solver
> (superlu_dist) and it ran, so the system apparently is not singular.
>
>     ILU can produce very badly conditioned (one could say singular
> PRECONDITIONER) from not singular sparse matrices. So it doesn't have
> anything to do with the system itself being singular.
>
>    What type of problem are you solving? Different problems need different
> preconditioners.
>
>   Barry
>
>
>
> >
> > Thanks in advance,
> > Eduardo
>
>
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