@Override
 protected void addEdges(KeyedGraph<? extends VCent, EdgeCent> graph) {
   graph.addEdge(1, 2);
   graph.addEdge(1, 3);
   graph.addEdge(1, 5);
   graph.addEdge(5, 2);
   graph.addEdge(2, 4);
   graph.addEdge(3, 4);
 }