Java Utililty Methods Gamma

List of utility methods to do Gamma

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Description

The list of methods to do Gamma are organized into topic(s).

Method

doublegammaFunction(double in)
Returns gamma value for a double in. 
if (in == 1.0) {
    return 1.0;
if (in == 0.5) {
    return Math.sqrt(Math.PI);
return (in - 1) * gammaFunction(in - 1);
doublegammaFwd(double lc)
gamma Fwd 
return (lc > 0.0031308) ? (1.055 * Math.pow(lc, 1 / 2.4) - 0.055) : (lc * 12.92);
doublegammaln(double x)
from numerical recipes in c (p. 
double ser = 1.00000000090015;
double y = x;
double tmp = x + 5.5;
tmp -= (x + 0.5) * Math.log(tmp);
for (int j = 0; j < 5; j++) {
    ser += COFGAMMALN[j] / ++y;
return -tmp + Math.log(ser * 2.5066282751072975 / x);
...
doublegammaOfArgOn2Plus1(int d)
Computes gamma(d/2 + 1) See http://en.wikipedia.org/wiki/Gamma_function for description of the analytical result for d odd. 
if (d % 2 == 0) {
    return factorialAsDouble(d / 2);
} else {
    return Math.sqrt(Math.PI) * (double) doubleFactorialAsDouble(d)
            / (double) Math.pow(2, ((double) (d + 1)) / 2.0);
doublegammaOfArgOn2Plus1IncludeDivisor(int d, double divisor)
Computes gamma(d/2 + 1)/divisor See http://en.wikipedia.org/wiki/Gamma_function for description of the analytical result for d odd. 
if (d % 2 == 0) {
    return factorialAsDoubleIncludeDivisor(d / 2, divisor);
} else {
    return doubleFactorialAsDoublewithDivisor(d,
            divisor * Math.pow(2, ((double) (d + 1)) / 2.0) / Math.sqrt(Math.PI));
doublegammaPdf(double x, double a)
gamma Pdf 
if (x <= 0.0) {
    return 0.0;
} else {
    return Math.exp(Math.log(x) * (a - 1) - x - lngamma(a));
doublegammaRand(double a)
Gamma random generator. 
double e, x, u0, u1, u2, v, w, c, c1, c2, c3, c4, c5;
boolean done;
e = Math.exp(1.0);
if (a < 1.0) {
    done = false;
    c = (a + e) / e;
    do {
        u0 = uniformRand();
...