/**
  * Get the distance from one Node to another Node in the graph.
  *
  * @param from The Node to get the distance from.
  * @param to The Node to get the distance to.
  * @return The distance between two Nodes
  */
 public double getDistance(Node from, Node to) {
   if (!distancesCalculated) {
     allPairsShortestPath = new AllPairsShortestPath(this);
     distancesCalculated = true;
   }
   return allPairsShortestPath.getDistance(from, to);
 }