Package etomica.math

Class Gamma

java.lang.Object

etomica.math.Gamma

public class Gamma
extends java.lang.Object

This class calculates the incomplete gamma function and complementary incomplete gamma function. This is a Java translation of Algorithm 542: Incomplete Gamma Functions [S14] by W. Gautschi from ACM Transactions on Mathematical Software (TOMS) Volume 5 , Issue 4 (December 1979) Pages: 482 - 489 see http://www.netlib.org/toms/542 The original algorithm was "taylored to the accuracy requirements of the CDC 6500 computer." Little to no attempt has been made to re-optimize for Java, other than to use Double.{MAX,MIN}_VALUE in place of defined constants.

Field Summary

Fields

Modifier and Type	Field	Description
protected static double	AL10
protected static double	ALPREC
protected static double	BOT
protected static int	BOTEXP
protected static double[]	C
protected static double[]	DBDEN
protected static double[]	DBNUM
protected static double	DC
protected double	G
protected double	GSTAR
protected int	IFLGST
protected static float	PREC
protected static double	TOP
protected static int	TOPEXP

Constructor Summary

Constructors

Constructor	Description
Gamma()

Method Summary

Modifier and Type	Method	Description
protected void	calcBoth(double A, double X)
double	calcGamma(double a, double x)	Return the normalized complementary incomplete gamma function, (integral from t=x to t=inf of exp(-t)*t^(a-1)) / gamma(a) if a>0 or (integral from t=x to t=inf of exp(-t)*t^(a-1)) * exp(x)*x^(-a) if a<=0
double	calcGammaStar(double a, double x)	Return the normalized incomplete gamma function, (integral from t=0 to t=x of exp(-t)*t^(a-1)) / x^a if a>0 If a=0 and x=0, gammaStar is indeterminate and an exception is thrown.
protected static double	DLGA(double DX)
double	getLastGamma()	Return the normalized complementary incomplete gamma function from the last calculation.
double	getLastGammaStar()	Return the normalized incomplete gamma function from the last calculation.
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

Field Detail

PREC

protected static final float PREC

See Also:

Constant Field Values

TOPEXP

protected static final int TOPEXP

BOTEXP

protected static final int BOTEXP

AL10

protected static final double AL10

ALPREC

protected static final double ALPREC

TOP

protected static final double TOP

BOT

protected static final double BOT

C

protected static final double[] C

G

protected double G

GSTAR

protected double GSTAR

IFLGST

protected int IFLGST

DBNUM

protected static final double[] DBNUM

DBDEN

protected static final double[] DBDEN

DC

protected static final double DC

Constructor Detail

Gamma

public Gamma()

Method Detail

calcGamma

public double calcGamma(double a,
                        double x)

Return the normalized complementary incomplete gamma function, (integral from t=x to t=inf of exp(-t)*t^(a-1)) / gamma(a) if a>0 or (integral from t=x to t=inf of exp(-t)*t^(a-1)) * exp(x)*x^(-a) if a<=0

calcGammaStar

public double calcGammaStar(double a,
                            double x)

Return the normalized incomplete gamma function, (integral from t=0 to t=x of exp(-t)*t^(a-1)) / x^a if a>0 If a=0 and x=0, gammaStar is indeterminate and an exception is thrown. gammaStar approaches 1 as x approaches 0 while a=0.

getLastGamma

public double getLastGamma()

Return the normalized complementary incomplete gamma function from the last calculation. This is useful if you called calcGammaStar, but now want gamma (gamma and gammaStar are both calculated).

getLastGammaStar

public double getLastGammaStar()

Return the normalized incomplete gamma function from the last calculation. This is useful if you called calcGamma, but now want gammaStar (gamma and gammaStar are both calculated).

calcBoth

protected void calcBoth(double A,
                        double X)

DLGA

protected static double DLGA(double DX)

main

public static void main(java.lang.String[] args)