<html><head></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><br><div><div>On Jan 27, 2012, at 12:18 PM, Jed Brown wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite"><div class="gmail_quote">On Fri, Jan 27, 2012 at 11:16, Anton Popov <span dir="ltr"><<a href="mailto:popov@uni-mainz.de">popov@uni-mainz.de</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
Does PETSc support repartitioning of coarse grid operators onto a smaller subset of processors during coarsening? Or the coarsest grid must be represented on the same amount of processors as the finest? It becomes a problem when a lot of processors are employed (say 4096 or more). If it is supported, how can I use it?</blockquote>
</div><br><div>PCGAMG does this automatically. There are some technical challenges to doing this with geometric multigrid, but we are thinking about how to do it best.</div>
</blockquote></div><br><div>GAMG does not repartition by default anymore -- it is very expensive. GAMG does now do simple process aggregation on coarser grids if repartitioning is not specified.</div></body></html>