All notes
Sigmoid

The sigmoid function, also called logistic function, is $y=\frac{1}{1+e^{-x}}$, which has an inflection point at $x=0$ (when $dy^2/d^2x = 0$). Its shape is the elongated 's', and it ranges from 0 (at $x=-\inf$) to 1 (at $x=\inf$).