org.apache.commons.math3.analysis.function

Class Sigmoid

java.lang.Object

org.apache.commons.math3.analysis.function.Sigmoid

All Implemented Interfaces:

DifferentiableUnivariateFunction, UnivariateDifferentiableFunction, UnivariateFunction

public class Sigmoid
extends java.lang.Object
implements UnivariateDifferentiableFunction, DifferentiableUnivariateFunction

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

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	Sigmoid.Parametric Parametric function where the input array contains the parameters of the sigmoid function, ordered as follows: Lower asymptote Higher asymptote

Field Summary

Fields

Modifier and Type	Field and Description
private double	hi Higher asymptote.
private double	lo Lower asymptote.

Constructor Summary

Constructors

Constructor and Description
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

Methods

Modifier and Type	Method and Description
UnivariateFunction	derivative() Deprecated. as of 3.1, replaced by value(DerivativeStructure)
DerivativeStructure	value(DerivativeStructure t) Simple mathematical function.
double	value(double x) Compute the value of the function.
private static double	value(double x, double lo, double hi)

Methods inherited from class java.lang.Object

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

Field Detail

lo

private final double lo

Lower asymptote.

hi

private final double hi

Higher asymptote.

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

@Deprecated
public UnivariateFunction derivative()

Deprecated. as of 3.1, replaced by value(DerivativeStructure)

Returns the derivative of the function

Specified by:

derivative in interface DifferentiableUnivariateFunction

Returns:

the derivative function

value

public double value(double x)

Compute the value of the function.

Specified by:

value in interface UnivariateFunction

Parameters:

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

Returns:

the value of the function.

value

private static double value(double x,
           double lo,
           double hi)

Parameters:

x - Value at which to compute the sigmoid.

lo - Lower asymptote.

hi - Higher asymptote.

Returns:

the value of the sigmoid function at x.

value

public DerivativeStructure value(DerivativeStructure t)
                          throws DimensionMismatchException

Simple mathematical function.

UnivariateDifferentiableFunction classes compute both the value and the first derivative of the function.

Specified by:

value in interface UnivariateDifferentiableFunction

Parameters:

t - function input value

Returns:

function result

Throws:

DimensionMismatchException - if t is inconsistent with the function's free parameters or order

Since:

3.1