[petsc-users] Issue using multi-grid as a pre-conditioner with KSP for a Poisson problem

[Jason Lefley]

Thanks for the clarification.

> On Jul 9, 2017, at 7:05 AM, Mark Adams <mfadams at lbl.gov> wrote:
> 
> 
> 
> What are the differences between gamg and mg with -pc_mg_galerkin option (apart from the default smoother/coarse grid solver options, which I identified by comparing the ksp_view output)? Perhaps there’s an issue with the restriction, as you suggest?
> 
> 
> Not sure if this got answered. GAMG is for unstructured problems. A "pure" AMG method. 
> 
> mg with -pc_mg_galerkin is semi-AMG, it still has geometric interpolation, and it is generally better if you can use it.

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