A sigmoid function is a generic term refering to S-like functions that have a step-like nature, but are smooth without the discontinuity of the threshold function. This maes them more emnable to use in machine learning as, in general, continuity aids learning.
Used in Chap. 6: page 87; Chap. 7: page 107; Chap. 9: pages 136, 137; Chap. 10: page 151; Chap. 21: page 357
Also known as sigmoid
Sigmoid function smoothly limits extreme values