class_docstr: Hypervolume calculator for any dimension.
  
  This class exactly calculates the hypervolume for any dimension by using the WFG algorithm.
  For detail, see `While, Lyndon, Lucas Bradstreet, and Luigi Barone. "A fast way of
  calculating exact hypervolumes." Evolutionary Computation, IEEE Transactions on 16.1 (2012)
  : 86-95.`.
code: def _compute(
      self, solution_set: np.ndarray, reference_point: np.ndarray
  ) -> float:
      self._reference_point = reference_point.astype(np.float64)
      return self._compute_rec(solution_set.astype(np.float64))
  
file_path: optuna/optuna/_hypervolume/wfg.py
imports: from typing import Optional
  import numpy
  from optuna._hypervolume import _compute_2d
  from optuna._hypervolume import _compute_2points_volume
  from optuna._hypervolume import BaseHypervolume
label_desc: Use image node_id 2 for calling the WFG obj's underlying member method code with example usage: obj._compute(solution_set, reference_point) and returns: self