The sigmoid function is one of the most popular nonlinear functions; it outputs 0 or 1 for any x input value between -∞ and +∞. The function can be mathematically and graphically expressed as follows:
Figure 4.7: Sigmoid function
The function curve takes an S shape and hence the name sigmoid. As we can see in this example, for the values of x between -2 and +2, the Y output values are very steep. A small change in the value of X in this region contributes significantly to the value of the output. This can be termed as an active gradient zone. For the purpose of simplicity, let's understand this as a region on the curve with ...
