code: def _xhat(x, mean, std, expander):
      x_mu = x - mean[expander]
      x_mu /= std[expander]
      return x_mu
  
imports: import warnings
  import numpy
  from chainer import backend
  from chainer.backends import cuda
  from chainer import configuration
  from chainer import function
  from chainer.functions.normalization import batch_normalization
  from chainer.utils import type_check
label_desc: Use image node_id 1 for calling a global function with example usage: _xhat(x, mean, std, expander) and returns: x_mu