code: def _normal_distribution_cdf(x, stddev):
      """Evaluates the CDF of the normal distribution.
  
      Normal distribution with mean 0 and standard deviation stddev,
      evaluated at x=x.
  
      input and output `Tensor`s have matching shapes.
  
      Args:
        x: a `Tensor`
        stddev: a `Tensor` with the same shape as `x`.
  
      Returns:
        a `Tensor` with the same shape as `x`.
  
      """
      return 0.5 * (1.0 + tf.erf(x / (math.sqrt(2) * stddev + 1e-20)))
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  import functools
  import math
  import six
  from six.moves import range
  from six.moves import zip
  from tensor2tensor.layers import common_layers
  from tensor2tensor.layers.vq_discrete import DiscreteBottleneck
  import tensorflow.compat.v1
label_desc: Use image node_id 6 for calling a global function with example usage: _normal_distribution_cdf(x, stddev) and returns: unknown