Inverse-decay exponentially from 0.01 to 1.0 reached at max_step.

def inverse_exp_decay(max_step, min_value=0.01, step=None):
  """Inverse-decay exponentially from 0.01 to 1.0 reached at max_step."""
  inv_base = tf.exp(tf.log(min_value) / float(max_step))
  if step is None:
    step = tf.train.get_global_step()
  if step is None:
    return 1.0
  step = to_float(step)
  return inv_base**tf.maximum(float(max_step) - step, 0.0)