[petsc-users] KSP convergence problem

[Jed Brown]

On Wed, Mar 20, 2013 at 2:00 PM, Mark F. Adams <mark.adams at columbia.edu>wrote:

>
> On Mar 20, 2013, at 2:12 PM, Mehrdad H Farahani <mh.farahani at gmail.com>
> wrote:
>
> > I'm experience a weird convergence problem with bcgsl with both ILU and
> GAMG preconditioning. The problem converges normally (at least in the
> preconditioned norm), but then kicks out with converged reason = -4. I've
> attached the convergence history of the previous time-step which worked and
> the timestep which shows problems. Could someone give me an idea on how to
> proceed?
> >
>
> Did you run with -ksp_converged_reason ?
>
> I don't know were this -4 comes from.  Could this be from your code?
>

Some people call KSPGetConvergedReason(), but then don't compare to the
enums and don't convert to a string using KSPConvergedReasons[reason].

http://www.mcs.anl.gov/petsc/petsc-dev/docs/manualpages/KSP/KSP_DIVERGED_DTOL.html

The problem is likely that your preconditioner is singular. What sort of
problem are you solving?
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