[petsc-users] Scaling problem when cores > 600

[Mark Adams]

>
>
> Or do I have to use KSPBCGS or KSPGMRES, which is directly from PETSc?
> However, I ran KSPGMRES yesterday with the Poisson eqn and my ans didn't
> converge.
>

As Matt said GMRES is not great for symmetric operators like Poisson and
you can use CG for the KSP method. HYPRE and GAMG are both fine
preconditioners. Try them both.

And I would suggest not worrying about scaling until you get a solver that
converges. Get your solver working well on small problems and as long as
you are not relying on fundamentally unscalable algorithms you should be
able to get scalability later.
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