From: Martin Kronbichler <martin.kronbichler@rub.de>
Date: Mon, 12 Feb 2024 12:13:23 +0000 (+0100)
Subject: MG transfer global coarsening: Avoid sending empty messages
X-Git-Tag: relicensing~33^2
X-Git-Url: https://gitweb.dealii.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=9f95e16348eb9d1fcba3262301cf5aa7b2d5c971;p=dealii.git

MG transfer global coarsening: Avoid sending empty messages
---

diff --git a/include/deal.II/multigrid/mg_transfer_global_coarsening.templates.h b/include/deal.II/multigrid/mg_transfer_global_coarsening.templates.h
index bb3e24d4b2..d3c154e0a1 100644
--- a/include/deal.II/multigrid/mg_transfer_global_coarsening.templates.h
+++ b/include/deal.II/multigrid/mg_transfer_global_coarsening.templates.h
@@ -866,7 +866,11 @@ namespace internal
 
         for (const auto &i : targets_with_indexset)
           {
-            if (i.first == my_rank)
+            // Skip communication in case we would send to ourselves or when
+            // there are no indices to send (this can still happen in the run
+            // of the consensus algorithms above if the index spaces are
+            // sparse).
+            if (i.first == my_rank || i.second.begin() == i.second.end())
               continue;
 
             indices_to_be_sent[i.first] = {};