[petsc-users] GAMG and zero pivots follow up

[Jed Brown]

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.

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.
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