The Sigmoid and its Derivative
The sigmoid function, \(\sigma(x)\), is also called the logistic function, or expit [1]. It is the inverse of the logit function. Its function definition is: \[ \sigma(x) = \frac{1}{1+e^{-x}} \tag{1}\] Let’s get familiar by plotting this function first: And just to be complete, here is the python code that produced the above plot: We see


