code: public static boolean hasNegativeCycle(Object sourceOrDest,
  			DirectedGraph g, Mode mode) {
  		return calcShortestDistances(sourceOrDest, g, mode) == null;
  	}
docs: Determines if there are any negative cycles found.
  
  @param sourceOrDest
  a vertex.
  @return <code>true</code> if a negative cycle was found,
  <code>false</code> otherwise.