code: @Override
    public int compareTo(EigenPair o) {
      if(this.eigenvalue < o.eigenvalue) {
        return -1;
      }
      if(this.eigenvalue > o.eigenvalue) {
        return +1;
      }
      return 0;
    }
docs: Compares this object with the specified object for order. Returns a
  negative integer, zero, or a positive integer as this object's eigenvalue
  is greater than, equal to, or less than the specified object's eigenvalue.
  
  @param o the Eigenvector to be compared.
  @return a negative integer, zero, or a positive integer as this object's
  eigenvalue is greater than, equal to, or less than the specified
  object's eigenvalue.