code: def FastGelu():
      r"""Returns a layer that computes a fast approximation to `Gelu`.
  
      .. math::
          f(x) = \frac{x}{2} \cdot (1 + \tanh(ax + abx^3))
  
      where :math:`a = 0.7978845608` and :math:`b = 0.044715`.
      """
  
      def f(x):  # pylint: disable=invalid-name
          return (
              0.5
              * x
              * (
                  1
                  + jnp.tanh(x * 0.7978845608 * (1 + 0.044715 * x * x))
              )
          )
  
      return Fn("FastGelu", f)
  
imports: from trax import fastmath
  from trax.fastmath import numpy
  from trax.layers import base
  from trax.layers.assert_shape import assert_shape
  from trax.layers.base import Fn
label_desc: Use image node_id 7 for calling a global function with example usage: FastGelu() and returns: Fn, unknown