org.apache.commons.math.analysis.function
Class Sigmoid

java.lang.Object
  org.apache.commons.math.analysis.function.Sigmoid

All Implemented Interfaces:

DifferentiableUnivariateRealFunction, UnivariateRealFunction

public class Sigmoid
extends java.lang.Object
implements DifferentiableUnivariateRealFunction

Sigmoid function. It is the inverse of the logit function. A more flexible version, the generalised logistic, is implemented by the Logistic class.

Since:

3.0

Version:

$Id$

Nested Class Summary

static class

Sigmoid.Parametric Parametric function where the input array contains the parameters of the logit function, ordered as follows: Lower asymptote Higher asymptote

Constructor Summary

Sigmoid()
Usual sigmoid function, where the lower asymptote is 0 and the higher asymptote is 1.

Sigmoid(double lo, double hi)
Sigmoid function.

Method Summary

UnivariateRealFunction	derivative() Returns the derivative of the function
double	value(double x) Compute the value of the function.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

Sigmoid

public Sigmoid()

Usual sigmoid function, where the lower asymptote is 0 and the higher asymptote is 1.

Sigmoid

public Sigmoid(double lo,
               double hi)

Sigmoid function.

Parameters:

lo - Lower asymptote.

hi - Higher asymptote.

Method Detail

derivative

public UnivariateRealFunction derivative()

Returns the derivative of the function

Specified by:

derivative in interface DifferentiableUnivariateRealFunction

Returns:

the derivative function

value

public double value(double x)

Compute the value of the function.

Specified by:

value in interface UnivariateRealFunction

Parameters:

x - Point at which the function value should be computed.

Returns:

the value of the function.