[petsc-users] Divergence termination of KSP iteration despite disabled convergence test

[Florian Rathgeber]

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Hi,

I instructed KSP (cg, jacobi) to run for a fixed number of CG iterations
(for benchmarking purposes) by disabling convergence testing and norm
computation as so:

    KSPSetConvergenceTest(ksp, KSPSkipConverged, PETSC_NULL, PETSC_NULL);
    KSPSetNormType(ksp, KSP_NORM_NO);

This worked fine for all my tests but Poisson. I tried solving Poisson
on P1, P2, and P3 elements with the right hand side 1 and no Dirichlet
condition (the result was not supposed to be meaningful, it was just for
benchmarking) and every time iteration terminated prematurely with
reason KSP_DIVERGED_INDEFINITE_MAT (-10).

To me, there are several strange issues with this:
1) I would expect KSPSkipConverged to disable the divergence check as well
2) I don't understand the divergence reason, how would the matrix
suddenly become indefinite?
3) Increasing the divergence limit to a very high value (1e50) doesn't
change anything

Could someone elaborate on these issues?

So my question is: how to safely disable this divergence test so that
KSP runs for the number of iterations I expect it to run?

Thank you for any hints

Florian
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