[petsc-dev] do all MIS algorithms require a symmetric structure?

[Mark Adams]

On Sun, Sep 18, 2022 at 4:02 PM Barry Smith <bsmith at 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
>
>
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