class_docstr: A class to compute different acquisition function values.
  
  Parameters
  ----------
  kind : string
      specification of utility function to use
  kappa : float
      parameter usedd for 'ucb' acquisition function
  xi : float
      parameter usedd for 'ei' and 'poi' acquisition function
code: def __init__(self, kind, kappa, xi):
      self._kappa = kappa
      self._xi = xi
  
      if kind not in ["ucb", "ei", "poi"]:
          err = (
              "The utility function "
              "{} has not been implemented, "
              "please choose one of ucb, ei, or poi.".format(kind)
          )
          raise NotImplementedError(err)
      self._kind = kind
  
file_path: nni/nni/algorithms/hpo/gp_tuner/util.py
imports: import warnings
  import numpy
  from scipy.stats import norm
  from scipy.optimize import minimize
label_desc: Use image node_id 1 to create a new UtilityFunction object  with example: obj = UtilityFunction(kind, kappa, xi)