Returns random data to be used with `feed_dict`.
  :param rng: A numpy.random.RandomState instance
  :param placeholders: List of tensorflow placeholders
  :return: A dict mapping placeholders to random numpy values

def random_feed_dict(rng, placeholders):
  """
  Returns random data to be used with `feed_dict`.
  :param rng: A numpy.random.RandomState instance
  :param placeholders: List of tensorflow placeholders
  :return: A dict mapping placeholders to random numpy values
  """

  output = {}

  for placeholder in placeholders:
    if placeholder.dtype != 'float32':
      raise NotImplementedError()
    value = rng.randn(*placeholder.shape).astype('float32')
    output[placeholder] = value

  return output