Sigmoid

Sigmoid activation function.

Transforms input 'x' according formula:

sigmoid(x) = 1 / (1 + exp(-x))

For small values (<-5), sigmoid returns a value close to zero, and for large values (>5) the result of the function gets close to 1.

NOTE: Sigmoid is equivalent to a 2-element Softmax, where the second element is assumed to be zero. The sigmoid function always returns a value between 0 and 1.

Calls SigmoidActivation under the hood.