code: public static int medoid(boolean parallel, List<? extends Vec> X, DistanceMetric dm)
      {
          return medoid(parallel, X, 1.0/X.size(), dm);
      }
docs: Computes the medoid of the data
  @param parallel whether or not the computation should be done using multiple cores
  @param X the list of all data
  @param dm the distance metric to get the medoid with respect to
  @return the index of the point in <tt>X</tt> that is the medoid