diff -r 4cade8579363 -r 7a98fe2ed989 lemon/floyd_warshall.h
--- a/lemon/floyd_warshall.h	Mon Oct 24 17:03:02 2005 +0000
+++ b/lemon/floyd_warshall.h	Wed Oct 26 10:50:47 2005 +0000
@@ -392,9 +392,9 @@
       for (NodeIt it(*graph); it != INVALID; ++it) {
 	for (NodeIt jt(*graph); jt != INVALID; ++jt) {
 	  _pred->set(it, jt, INVALID);
-	  _dist->set(it, jt, it == jt ? 
-		     OperationTraits::zero() : OperationTraits::infinity());
+	  _dist->set(it, jt, OperationTraits::infinity());
 	}
+	_dist->set(it, it, OperationTraits::zero());
       }
       for (EdgeIt it(*graph); it != INVALID; ++it) {
 	Node source = graph->source(it);
@@ -427,6 +427,24 @@
 	}
       }
     }
+
+    /// \brief Executes the algorithm and checks the negative circles.
+    ///
+    /// This method runs the %FloydWarshall algorithm in order to compute 
+    /// the shortest path to each node pairs. If there is a negative circle 
+    /// in the graph it gives back false. 
+    /// The algorithm computes 
+    /// - The shortest path tree for each node.
+    /// - The distance between each node pairs.
+    bool checkedStart() {
+      start();
+      for (NodeIt it(*graph); it != INVALID; ++it) {
+	if (OperationTraits::less((*dist)(it, it), OperationTraits::zero())) {
+	  return false;
+	}
+      }
+      return true;
+    }
     
     /// \brief Runs %FloydWarshall algorithm.
     ///