code: public static <S extends Solution<?>> double[][] distanceMatrix(List<S> solutionSet) {
      double[][] distance = new double[solutionSet.size()][solutionSet.size()];
      for (int i = 0; i < solutionSet.size(); i++) {
        distance[i][i] = 0.0;
        for (int j = i + 1; j < solutionSet.size(); j++) {
          distance[i][j] = SolutionUtils.distanceBetweenObjectives(solutionSet.get(i), solutionSet.get(j));
          distance[j][i] = distance[i][j];
        }
      }
      return distance;
    }
docs: Returns a matrix with the euclidean distance between each pair of solutions in the population.
  Distances are measured in the objective space
  
  @param solutionSet
  @return