/*
* BioJava development code
*
* This code may be freely distributed and modified under the
* terms of the GNU Lesser General Public Licence. This should
* be distributed with the code. If you do not have a copy,
* see:
*
* http://www.gnu.org/copyleft/lesser.html
*
* Copyright for this code is held jointly by the individual
* authors. These should be listed in @author doc comments.
*
* For more information on the BioJava project and its aims,
* or to join the biojava-l mailing list, visit the home page
* at:
*
* http://www.biojava.org/
*
*/
package org.biojava.nbio.survival.cox.stats;
/**
*
* @author Scooter Willis <willishf at gmail dot com>
*/
public class ChiSq {
/**
*
* @param z
* @return
*/
public static double norm(double z) {
return ChiSq.chiSq(z * z, 1);
}
/**
*
* @param x
* @param n
* @return
*/
public static double chiSq(double x, int n) {
double p = Math.exp(-0.5 * x);
if ((n % 2) == 1) {
p = p * Math.sqrt(2 * x / Math.PI);
}
double k = n;
while (k >= 2) {
p = p * x / k;
k = k - 2;
}
double t = p;
double a = n;
while (t > 0.000001 * p) {
a = a + 2;
t = t * x / a;
p = p + t;
}
return 1 - p;
}
/**
* @param args the command line arguments
*/
public static void main(String[] args) {
// TODO code application logic here
}
}