> > > > 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.
