org.terrier.statistics

Class GammaFunction

java.lang.Object

org.terrier.statistics.GammaFunction

All Implemented Interfaces:

Serializable

public abstract class GammaFunction
extends Object
implements Serializable

Base class for implementations of the Gamma function. Use getGammaFunction() to obtain an instance. The exact instance can be controlled by property gamma.function For consistency when computing logarithms of the gamma function, all implementations assume positive input values. In practice, as the gamma function can generate large values, normal usage should use compute_log() anyway.

Properties:

• gamma.function - class name of the Gamma function implementation.

Defaults to use WikipediaLanczosGammaFunction

Since:

3.0

Author:

Craig Macdonald

See Also:

Serialized Form

Constructor Summary

Constructors

Constructor and Description
GammaFunction()

Method Summary

Modifier and Type	Method and Description
abstract double	compute_log(double number) Get the value of the log of gamma function for the specified number.
abstract double	compute(double number) Get the value of the gamma function for the specified number.
static long	factorial(long n) Compute factorial of n, for 0 < n < 21.
static GammaFunction	getGammaFunction() Obtain an instance of GammaFunction
static void	main(String[] args)

Methods inherited from class java.lang.Object

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

Constructor Detail

GammaFunction

public GammaFunction()

Method Detail

compute

public abstract double compute(double number)

Get the value of the gamma function for the specified number.

Parameters:

number - for which is required

Returns:

(n-1)!

compute_log

public abstract double compute_log(double number)

Get the value of the log of gamma function for the specified number.

Parameters:

number - for which is required

Returns:

log(n-1)!

getGammaFunction

public static final GammaFunction getGammaFunction()

Obtain an instance of GammaFunction

main

public static void main(String[] args)

factorial

public static final long factorial(long n)

Compute factorial of n, for 0 < n < 21.

Parameters:

n - number to compute for

Returns:

factorial of n