[petsc-users] GAMG and zero pivots follow up

[Matthew Knepley]

On Fri, Nov 13, 2015 at 12:28 PM, Jed Brown <jed at jedbrown.org> wrote:

> Matthew Knepley <knepley at gmail.com> writes:
> > Something very strange is happening here. CG should converge
> monotonically,
> > but above it does not. What could be happening?
>
> Are you use -ksp_norm_type natural?  CG is not monotone in other norms.
>

Yikes! I did not check that. Why do we have PRECONDITIONED as the default
for CG?

   Matt

Also, if boundary conditions are enforced using a nonsymmetric
> formulation (for example), then you can get lack of monotonicity with CG
> that may not be catastrophic.
>



-- 
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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