code: def Swish():
      r"""Returns a layer that computes the Swish function.
  
      .. math::
          f(x) = x \cdot \text{sigmoid}(x)
      """
      return Fn("Swish", lambda x: x * fastmath.expit(x))
  
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 15 for calling a global function with example usage: Swish() and returns: Fn