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 <[email protected]> wrote:
>
>
>
> On Sun, Sep 18, 2022 at 4:02 PM Barry Smith <[email protected]
> <mailto:[email protected]>> 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
>
