[petsc-users] GAMG processor reduction

[Jed Brown]

Mark Adams <mfadams at lbl.gov> writes:

> '-pc_gamg_verbose 2' will print out stuff where you can see the number of
> active processors.  We have not been super motivated to use subcoms because
> there are no norms taken on coarse grids, except in the eigen estimator for
> cheby, unless you use krylov in the solver, which is not usually useful.
> Jed: GAMG does reduce active processors by default.  I'm pretty sure.  

Yup, it reduces the active process set, but does not create a subcomm,
There are no reductions (inner products or norms) on the coarse grid in
the current configuration.  Iterative coarse solvers would be a good
reason to create a subcomm.
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