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<p style="margin-top:0;margin-bottom:0">Dear Vatslav,</p>
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<p style="margin-top:0;margin-bottom:0">Genmap uses recursive spectral bisection to partition the mesh into successively smaller subsets. In principle, each cut should have minimally-sized separators so that communication is small. In addition, the load should
be balanced, meaning that the number of elements in each of the two newly-generated subsets should differ by at most 1.</p>
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<p style="margin-top:0;margin-bottom:0">A consequence of the first of these aims is that each newly-created subdomain should be connected. (In other words, the cut generates at most 2 separated subgraphs.)</p>
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<p style="margin-top:0;margin-bottom:0">It's easy to show that there are some small subgraphs where all of these conditions cannot be met. It can also happen on larger subgraphs---which is where it become problematic because the communication overhead can
then start to be quite large. So, we have genmap flag cases whenever one of the new subgraphs is not connected.</p>
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<p style="margin-top:0;margin-bottom:0">In your case, the small integers indicate that the cut in question is near the bottom of the partition tree--in effect at the leaves--so all is ok. There will be no adverse consequences.</p>
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<p style="margin-top:0;margin-bottom:0">hth</p>
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<p style="margin-top:0;margin-bottom:0">Paul</p>
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<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" style="font-size:11pt" color="#000000"><b>From:</b> Nek5000-users <nek5000-users-bounces@lists.mcs.anl.gov> on behalf of nek5000-users@lists.mcs.anl.gov <nek5000-users@lists.mcs.anl.gov><br>
<b>Sent:</b> Wednesday, March 28, 2018 11:56:05 PM<br>
<b>To:</b> nek5000-users@lists.mcs.anl.gov<br>
<b>Subject:</b> [Nek5000-users] genmap for 130k elements</font>
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<div>Hi all,<br>
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<div>Now I am trying to build the mesh with more than 130k elements, so I find out that genmap can not process properly the mesh. I catch the errors like:<br>
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' not connected 1 4 5 0 '.<br>
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<div>But when I reduce the number of elements to ~ 129k it works great.<br>
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<div>Is it a bug or I must use some flag ?<br>
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Regards,<br>
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Vatslav<br>
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