<div class="gmail_extra">On Wed, Apr 25, 2012 at 3:21 AM, Thomas Witkowski <span dir="ltr"><<a href="mailto:thomas.witkowski@tu-dresden.de" target="_blank">thomas.witkowski@tu-dresden.de</a>></span> wrote:<br><div class="gmail_quote">
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Is it possible to create a parallel matrix (MPIAIJ) with empty size on some ranks? Even if this should work, does it make sense (with respect to runtime and efficiency) to collect all ranks having a nonempty contribution the the global matrix in an mpi group and to use this communicator for matrix create/computations?</blockquote>
<div><br></div><div>1) Yes</div><div><br></div><div>2) It depends. If there are a bunch of empty procs and you do reductions, it may make sense to leave them out. But</div><div> you would have to be on a large number of processes.</div>
<div><br></div><div> Matt</div><div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><span class="HOEnZb"><font color="#888888"><br>
Thomas<br>
</font></span></blockquote></div><br><br clear="all"><div><br></div>-- <br>What most experimenters take for granted before they begin their experiments is infinitely more interesting than any results to which their experiments lead.<br>
-- Norbert Wiener<br>
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