## FANDOM

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A sigmoid function is a function whose graph is shaped like the letter S. It could be defined as a differentiable bijection $f$ from the real numbers to an open interval $(a,b)$ , with $\lim_{x\to\infty}f(x)=b\ ,\ \lim_{x\to-\infty} f(x)=a$ .

"The" sigmoid function $S(x)=\frac{1}{1+e^{-x}}$ , a special case of the logistic function. Other sigmoid functions include arctan and erf.

One application of sigmoid functions is neural networks in AI programming.