function elu$2(args) {
	  return new ELU(args);
	}
Exponetial Linear Unit (ELU).

It follows:
`f(x) =  alpha * (exp(x) - 1.) for x < 0`,
`f(x) = x for x >= 0`.

Input shape:
  Arbitrary. Use the configuration `inputShape` when using this layer as the
  first layer in a model.

Output shape:
  Same shape as the input.

References:
  - [Fast and Accurate Deep Network Learning by Exponential Linear Units
(ELUs)](https://arxiv.org/abs/1511.07289v1)

@doc {
  heading: 'Layers',
  subheading: 'Advanced Activation',
  namespace: 'layers'
}