code: public <E extends Edge> MultiMap<Integer,Integer> cluster(
                        final Graph<E> graph, int numClusters, Properties props) {
          return singleLink(graph, numClusters);
          // throw new Error();
      }
docs: Computes the similarity of the graph's edges and merges them until the
  specified number of clusters has been reached.
  
  @param numClusters the number of clusters to return