# HG changeset patch
# User Peter Kovacs <kpeter@inf.elte.hu>
# Date 1376944554 -7200
# Node ID b40c2bbb8da5210894426e3c4405b8a6d6d50d22
# Parent  fb932bcfd803e4ed14c9d750d924a09eb230aadd
Fix division by zero error in case of empty graph (#474)

diff -r fb932bcfd803 -r b40c2bbb8da5 lemon/network_simplex.h
--- a/lemon/network_simplex.h	Sat Sep 04 23:58:03 2010 +0200
+++ b/lemon/network_simplex.h	Mon Aug 19 22:35:54 2013 +0200
@@ -929,7 +929,7 @@
       for (NodeIt n(_graph); n != INVALID; ++n, ++i) {
         _node_id[n] = i;
       }
-      if (_arc_mixing) {
+      if (_arc_mixing && _node_num > 1) {
         // Store the arcs in a mixed order
         const int skip = std::max(_arc_num / _node_num, 3);
         int i = 0, j = 0;
diff -r fb932bcfd803 -r b40c2bbb8da5 test/min_cost_flow_test.cc
--- a/test/min_cost_flow_test.cc	Sat Sep 04 23:58:03 2010 +0200
+++ b/test/min_cost_flow_test.cc	Mon Aug 19 22:35:54 2013 +0200
@@ -395,6 +395,12 @@
   mcf3.upperMap(neg2_u);
   checkMcf(mcf3, mcf3.run(param), neg2_gr, neg2_l, neg2_u, neg2_c, neg2_s,
            mcf3.OPTIMAL, true,     -300, test_str + "-18", GEQ);
+
+  // Tests for empty graph
+  Digraph gr0;
+  MCF mcf0(gr0);
+  mcf0.run(param);
+  check(mcf0.totalCost() == 0, "Wrong total cost");  
 }
 
 template < typename MCF, typename Param >