The Sigmoid Function (the logistic function)
The sigmoid function is a continuous, monotonically increasing function with a characteristic 'S'-like curve, and possesses several interesting properties that make it an obvious choice as an activation function for nodes in artificial neural networks.
The domain of the sigmoid function is the set of all real numbers, , and it's defined as:
Please note that equation could just as well be written as (this is seen by multiplying equation (1) by , i.e. multiplying by 1).
Please note that equation could just as well be written as (this is seen by multiplying equation (1) by , i.e. multiplying by 1).
The graph of the sigmoid function illustrates its smooth, gradual transition from values just above to values just below - a transition that almost fully occurs in the interval .
For arguments near the sigmoid function approximates a linear function with slope .
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