code: def forward_cpu(self, inputs):
      self.retain_inputs((0,))
      (x,) = inputs
      x_hat = x - self.mean[:, None]
      x_hat *= self.inv_std[:, None]
      self.retain_outputs((0,))
      return (x_hat,)
  
imports: import numpy
  import chainer
  from chainer import backend
  from chainer.backends import cuda
  from chainer import configuration
  from chainer import function_node
  from chainer.utils import type_check
label_desc: Use image node_id 2 for calling the _XHat obj's underlying member method code with example usage: obj.forward_cpu(inputs) and returns: x_hat