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

java.lang.Object
  extended by org.apache.commons.math3.analysis.function.Sigmoid
All Implemented Interfaces:
DifferentiableUnivariateFunction, UnivariateFunction

public class Sigmoid
extends Object
implements 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
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
 
Field Summary
private  double hi
          Higher asymptote.
private  double lo
          Lower 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
 UnivariateFunction derivative()
          Returns the derivative of the 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

public UnivariateFunction derivative()
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.


Copyright (c) 2003-2013 Apache Software Foundation