code: public List<Double> mean() {
      List<Double> result = new ArrayList<>(this.numberOfObjectives);
      for (int i = 0; i < this.numberOfObjectives; i++)
        result.add(0.0);
  
      for (List<Double> historyMember : this.history)
        for (int i = 0; i < this.numberOfObjectives;i++)
          result.set(i, result.get(i) + historyMember.get(i));
  
  
      for (int i = 0; i < this.numberOfObjectives; i++)
        result.set(i, result.get(i)/(double)this.history.size());
  
      return result;
    }
docs: Returns the mean of the values contained in the history