class_docstr: A CEM class, inherited from Optimizer.
  
  This is the designed class to define CEM-related
  variables and methods.
  
  References:
      R. Y. Rubinstein. Optimization of Computer simulation Models with Rare Events.
      European Journal of Operations Research (1997).
docstr: Array of means.
docstr_tok: ["Array","of","means","."]
code: def mean(self) -> np.ndarray:
      """Array of means."""
  
      return self._mean
  
imports: from typing import Any, Dict, List, Optional
  import numpy
  import opytimizer.math.random
  import opytimizer.utils.exception
  from opytimizer.core import Optimizer
  from opytimizer.core.agent import Agent
  from opytimizer.core.function import Function
  from opytimizer.core.space import Space
  from opytimizer.utils import logging
label_desc: Use image node_id 6 for calling the CEM obj's underlying member method code with example usage: obj.mean() and returns: self