Definition:Sigmoid Curve
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Definition
A sigmoid curve is a plane curve which:
- is the locus of a (strictly) increasing real function
- has two horizontal asymptotes
- has exactly one point of inflection.
Examples
Also known as
A sigmoid curve is also known as an S-shaped curve, after the shape of an archaic English $S$, that is: $\int$.
It is also known as the logistic curve, which is a specific instance of a sigmoid curve.
Also see
- Results about sigmoid curves can be found here.
Linguistic Note
The word sigmoid derives from the Greek letter "Sigma", and means S-shaped.
This derives from the archaic form of the English letter $S$, still in use as the integral sign $\int$.
Sources
- 1998: David Nelson: The Penguin Dictionary of Mathematics (2nd ed.) ... (previous) ... (next): sigmoid curve
- 2008: David Nelson: The Penguin Dictionary of Mathematics (4th ed.) ... (previous) ... (next): sigmoid curve