code: public Map<Integer, Integer> getDegreeDistribution() {
          if (degreeDistribution == null) {    // has not been initialized
              logger.debug("Calling setGraphParameters");
              setGraphParameters();
          }
          return degreeDistribution;
      }
docs: Computes the degree distribution. The degree of a node is the number of edges that it is connected with.
  The graph is treated as an undirected graph.
  Computing graph parameters requires touching all node pairs.
  Therefore, if one is called the others are computed as well and stored for later retrieval.
  @return A map with the degree distribution of the graph.