Sigmoid Function
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The sigmoid function, also called the sigmoidal curve (von Seggern 2007, p. 148) or logistic function, is the function
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(1)
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It has derivative
 |  | ![[1-y(x)]y(x)](/images/equations/SigmoidFunction/Inline3.gif) |
(2)
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(3)
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(4)
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(5)
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(6)
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It has Maclaurin series
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(7)
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(8)
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(9)
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where 
is an Euler
polynomial and 
is a Bernoulli
number.
It has an inflection point at 
, where
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(10)
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It is also the solution to the ordinary differential equation
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(11)
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with initial condition 
.
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sigmoid function
