<html><head><meta http-equiv="Content-Type" content="text/html; charset=us-ascii"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class=""><div class=""><br class=""></div> Mark,<div class=""><br class=""></div><div class=""> 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 </div><div class="">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.</div><div class=""><br class=""></div><div class=""><br class=""><div><br class=""><blockquote type="cite" class=""><div class="">On Sep 18, 2022, at 4:21 PM, Mark Adams <<a href="mailto:mfadams@lbl.gov" class="">mfadams@lbl.gov</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div dir="ltr" class=""><div dir="ltr" class=""><br class=""></div><br class=""><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Sun, Sep 18, 2022 at 4:02 PM Barry Smith <<a href="mailto:bsmith@petsc.dev" class="">bsmith@petsc.dev</a>> wrote:<br class=""></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><br class="">
Mark,<br class="">
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Do all MIS algorithms in PETSc require a symmetric graph structure? And parallel ones can hang if not structurally symmetric?<br class=""></blockquote><div class=""><br class=""></div><div class="">Yes,</div><div class=""> </div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
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When used sequentially I guess it never hangs but it may not produce a "correct" MIS if the matrix structure is not symmetric?</blockquote><div class=""><br class=""></div><div class="">It is fine in serial and it is not necessarily an MIS of the symmetrized graph.</div><div class="">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.</div><div class=""> </div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"> But like the MIS is fine for GAMG in this circumstance?<br class=""></blockquote><div class=""><br class=""></div><div class="">It will be fine for GAMG. The MIS is just a heuristic.</div><div class=""> </div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
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Barry<br class="">
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