From 2d315d45824dfe237a38de864139e0bfb9fed58d Mon Sep 17 00:00:00 2001
From: Tiago de Paula Peixoto <tiago@skewed.de>
Date: Sun, 3 Nov 2013 11:11:21 +0100
Subject: [PATCH] Forbid creation of empty blocks in mcmc_sweep()

---
 src/graph/community/graph_blockmodel.hh | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/src/graph/community/graph_blockmodel.hh b/src/graph/community/graph_blockmodel.hh
index d86a6eb3..c2d99e0d 100644
--- a/src/graph/community/graph_blockmodel.hh
+++ b/src/graph/community/graph_blockmodel.hh
@@ -1197,6 +1197,10 @@ void move_sweep(EMprop mrs, Vprop mrp, Vprop mrm, Vprop wr, Vprop b,
         vertex_t v = vertex(vlist[i], g);
         vertex_t r = b[v];
 
+        // blocks can't become empty
+        if (wr[r] == 1)
+            continue;
+
         if (!sequential)
             moves[i] = r;
 
-- 
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