/* Copyright (C) 2003 Univ. of Massachusetts Amherst, Computer Science Dept.
This file is part of "MALLET" (MAchine Learning for LanguagE Toolkit).
http://www.cs.umass.edu/~mccallum/mallet
This software is provided under the terms of the Common Public License,
version 1.0, as published by http://www.opensource.org. For further
information, see the file `LICENSE' included with this distribution. */
//package cc.mallet.util;
/**
*
*
* @author <a href="mailto:[email protected]">Charles Sutton</a>
* @version $Id: ArrayUtils.java,v 1.1 2007/10/22 21:37:40 mccallum Exp $
*/
public class Util {
public static double logBeta (double a, double b) {
return logGamma(a)+logGamma(b)-logGamma(a+b);
}
// From libbow, dirichlet.c
// Written by Tom Minka <[email protected]>
public static final double logGamma (double x)
{
double result, y, xnum, xden;
int i;
final double d1 = -5.772156649015328605195174e-1;
final double p1[] = {
4.945235359296727046734888e0, 2.018112620856775083915565e2,
2.290838373831346393026739e3, 1.131967205903380828685045e4,
2.855724635671635335736389e4, 3.848496228443793359990269e4,
2.637748787624195437963534e4, 7.225813979700288197698961e3
};
final double q1[] = {
6.748212550303777196073036e1, 1.113332393857199323513008e3,
7.738757056935398733233834e3, 2.763987074403340708898585e4,
5.499310206226157329794414e4, 6.161122180066002127833352e4,
3.635127591501940507276287e4, 8.785536302431013170870835e3
};
final double d2 = 4.227843350984671393993777e-1;
final double p2[] = {
4.974607845568932035012064e0, 5.424138599891070494101986e2,
1.550693864978364947665077e4, 1.847932904445632425417223e5,
1.088204769468828767498470e6, 3.338152967987029735917223e6,
5.106661678927352456275255e6, 3.074109054850539556250927e6
};
final double q2[] = {
1.830328399370592604055942e2, 7.765049321445005871323047e3,
1.331903827966074194402448e5, 1.136705821321969608938755e6,
5.267964117437946917577538e6, 1.346701454311101692290052e7,
1.782736530353274213975932e7, 9.533095591844353613395747e6
};
final double d4 = 1.791759469228055000094023e0;
final double p4[] = {
1.474502166059939948905062e4, 2.426813369486704502836312e6,
1.214755574045093227939592e8, 2.663432449630976949898078e9,
2.940378956634553899906876e10, 1.702665737765398868392998e11,
4.926125793377430887588120e11, 5.606251856223951465078242e11
};
final double q4[] = {
2.690530175870899333379843e3, 6.393885654300092398984238e5,
4.135599930241388052042842e7, 1.120872109616147941376570e9,
1.488613728678813811542398e10, 1.016803586272438228077304e11,
3.417476345507377132798597e11, 4.463158187419713286462081e11
};
final double c[] = {
-1.910444077728e-03, 8.4171387781295e-04,
-5.952379913043012e-04, 7.93650793500350248e-04,
-2.777777777777681622553e-03, 8.333333333333333331554247e-02,
5.7083835261e-03
};
final double a = 0.6796875;
if((x <= 0.5) || ((x > a) && (x <= 1.5))) {
if(x <= 0.5) {
result = -Math.log(x);
/* Test whether X < machine epsilon. */
if(x+1 == 1) {
return result;
}
}
else {
result = 0;
x = (x - 0.5) - 0.5;
}
xnum = 0;
xden = 1;
for(i=0;i<8;i++) {
xnum = xnum * x + p1[i];
xden = xden * x + q1[i];
}
result += x*(d1 + x*(xnum/xden));
}
else if((x <= a) || ((x > 1.5) && (x <= 4))) {
if(x <= a) {
result = -Math.log(x);
x = (x - 0.5) - 0.5;
}
else {
result = 0;
x -= 2;
}
xnum = 0;
xden = 1;
for(i=0;i<8;i++) {
xnum = xnum * x + p2[i];
xden = xden * x + q2[i];
}
result += x*(d2 + x*(xnum/xden));
}
else if(x <= 12) {
x -= 4;
xnum = 0;
xden = -1;
for(i=0;i<8;i++) {
xnum = xnum * x + p4[i];
xden = xden * x + q4[i];
}
result = d4 + x*(xnum/xden);
}
/* X > 12 */
else {
y = Math.log(x);
result = x*(y - 1) - y*0.5 + .9189385332046727417803297;
x = 1/x;
y = x*x;
xnum = c[6];
for(i=0;i<6;i++) {
xnum = xnum * y + c[i];
}
xnum *= x;
result += xnum;
}
return result;
}
}
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