class_docstr: An NDS class, inherited from Optimizer.
  
  This is the designed class to define NDS-related
  variables and methods.
  
  References:
      P. Godfrey, R. Shipley and J. Gryz.
      Algorithms and Analyses for Maximal Vector Computation.
      The VLDB Journal (2007).
docstr: Number of points in the frontier.
docstr_tok: ["Number","of","points","in","the","frontier","."]
code: def n_pareto_points(self) -> int:
      """Number of points in the frontier."""
  
      return self._n_pareto_points
  
imports: import copy
  from typing import Any, Dict, Optional
  import numpy
  import opytimizer.utils.exception
  from opytimizer.core import Optimizer
  from opytimizer.core.agent import Agent
  from opytimizer.core.space import Space
  from opytimizer.utils import logging
label_desc: Use image node_id 2 for calling the NDS obj's underlying member method code with example usage: obj.n_pareto_points() and returns: self