torch.nn.functional.softplus
torch.nn.functional.softplus(input, beta=1, threshold=20) -> Tensor
Applies element-wise, the function \text{Softplus}(x) =
   \frac{1}{\beta} * \log(1 + \exp(\beta * x)).
For numerical stability the implementation reverts to the linear
   function when input \times \beta > threshold.
See "Softplus" for more details.