Right, but I want to run with the old options MIS (instead of MIS-2) and get the same times as before. But instead I am getting much larger times.
> On Sep 18, 2022, at 6:58 PM, Mark Adams <mfad...@lbl.gov> wrote: > > > > On Sun, Sep 18, 2022 at 6:19 PM Barry Smith <bsm...@petsc.dev > <mailto:bsm...@petsc.dev>> wrote: > > Mark, > > Some how your changes to GAMG in June slowed down the time to compute the > MIS dramatically. I cannot figure out what options to use to > get the exact same performance as an older branch. -mat_coarsen_type mis > -pc_gamg_threshold 0 result in longer times than the older code with its > default options. > > The new MIS-2 folds in the square graph with the MIS. Before the square graph > was in a separate method that created an squared graph explicitly. So don't > use aggressive coarsening (you will see a PtAP if you use aggressive > coarsening in the new code) > And -pc_gamg_threshold 0 will filter (zeros only). Use < 0 for no filtering. > The old code also had this optimization to not create a graph for bs==1 and > no filter, > > Mark > > > > >> On Sep 18, 2022, at 4:21 PM, Mark Adams <mfad...@lbl.gov >> <mailto:mfad...@lbl.gov>> wrote: >> >> >> >> On Sun, Sep 18, 2022 at 4:02 PM Barry Smith <bsm...@petsc.dev >> <mailto:bsm...@petsc.dev>> wrote: >> >> Mark, >> >> Do all MIS algorithms in PETSc require a symmetric graph structure? And >> parallel ones can hang if not structurally symmetric? >> >> Yes, >> >> >> When used sequentially I guess it never hangs but it may not produce a >> "correct" MIS if the matrix structure is not symmetric? >> >> It is fine in serial and it is not necessarily an MIS of the symmetrized >> graph. >> If there is a one way edge between two vertices and the order of the greedy >> MIS process picks the root of the edge it is an MIS of the symmetrized >> graph, otherwise both vertices could get selected. >> >> But like the MIS is fine for GAMG in this circumstance? >> >> It will be fine for GAMG. The MIS is just a heuristic. >> >> >> Barry >> >
