code: def itransform(self, y):
      y = y.astype(self.float_type)
      y = 2 * y / self.mu - 1
      x = numpy.sign(y) / self.mu * ((1 + self.mu) ** numpy.abs(y) - 1)
      return x.astype(self.float_type)
  
file_path: chainer/examples/wavenet/utils.py
imports: import random
  import librosa
  import numpy
  import chainer
label_desc: Use image node_id 3 for calling the MuLaw obj's underlying member method code with example usage: obj.itransform(y) and returns: x