Main Page | See live article | Alphabetical index "Sigmoid" means resembling the letter S or the lower-case Greek letter sigma (ς). In a neural network, the sigmoid function is used to add nonlinearity. A bounded sigmoid function is the hyperbolic tangent function, or this translated to the range (0,1); an unbounded sigmoid function is the inverse hyperbolic cosine function. See also: Sigmoid function This article is from Wikipedia. All text is available under the terms of the GNU Free Documentation License.