Re: [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 <mfad...@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.