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.
> On Sep 18, 2022, at 4:21 PM, Mark Adams <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 >