On Thu, Jul 19, 2018 at 9:44 PM Weston, Brian Thomas <[email protected]> wrote:
> Hi Mark, > > I’m using the default settings with GAMG for 2D problems and it’s > performing much worse than BoomerAMG for my problem. I was told, however, > that GAMG’s defaults were optimized for 3D problems, so I was wondering if > you knew of better settings for 2D or which knobs might be most significant > to play with? Is pc mg levels the way to control the number of aggressive > coarsening levels? I tried using unsmoothed aggregation, but it was only > marginally better than the default. > Are you looking at iteration count or solve time? This is a 5-point stencil. You want to square the graph: '-pc_gamg_square_graph 20' (20 is the number of levels to square the graph, which is infinity really). You can use: -mg_levels_ksp_type richardson -mg_levels_pc_type sor and one processor this is a prefect smoother, just for debugging. And you can run with -info and grep on GAMG and send me the result (about 20 lines). This should give me an idea of what is wrong if these ideas don't work. Mark > The discretization is a essentially a 2nd-order cell-centered > finite-volume scheme and I’m primarily solving a pressure-velocity Schur > complement system. > > best, > Brian
