GammaFunction (Terrier Information Retrieval Platform 5.5 API)

java.lang.Object
- org.terrier.statistics.GammaFunction

All Implemented Interfaces:

java.io.Serializable
```
public abstract class GammaFunction
extends java.lang.Object
implements java.io.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 Description

GammaFunction()

Method Summary

All Methods Static Methods Instance Methods Abstract Methods Concrete Methods
Modifier and Type	Method	Description
`abstract double`	`compute(double number)`	Get the value of the gamma function for the specified number.
`abstract double`	`compute_log(double number)`	Get the value of the log of 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(java.lang.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(java.lang.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