Returns chi-square probability. - Java java.lang

Java examples for java.lang:Math Function

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Description

Returns chi-square probability.

Demo Code


//package com.java2s;

public class Main {
    /**/*from w w  w .j  av  a  2 s  .  co m*/
     * Returns chi-square probability.
     */
    public static double chiSquareProb(int number, double value) {
        if (number % 2 == 0) {
            return chiSquareProbEven(number, value);
        } else {
            return chiSquareProbOdd(number, value);
        }
    }

    /**
     * Returns chi-square probability for even numbers number.
     */
    public static double chiSquareProbEven(int number, double value) {
        double result = 0;
        for (int idx = 0; idx <= (number / 2 - 1); idx++) {
            result += (1 / gammaFunction(idx + 1))
                    * Math.pow(value / 2, idx);
        }
        return Math.exp(-value / 2) * result;
    }

    /**
     * Returns chi-square probability for odd numbers number.
     */
    public static double chiSquareProbOdd(int number, double value) {
        double result = 0;
        for (int idx = 0; idx <= (number / 2 - 1); idx++) {
            result += (1 / gammaFunction(idx + 1.5))
                    * Math.pow(value / 2, idx + 0.5);
        }
        return errFunction(Math.sqrt(value / 2)) - Math.exp(-value / 2)
                * result;
    }

    /**
     * Returns gamma value for a double in.
     */
    public static double gammaFunction(double in) {
        if (in == 1.0) {
            return 1.0;
        }
        if (in == 0.5) {
            return Math.sqrt(Math.PI);
        }
        return (in - 1) * gammaFunction(in - 1);
    }

    /**
     * Returns error function for given double in.
     */
    public static double errFunction(double in) {
        return (2 / Math.sqrt(Math.PI)) * Math.exp(-in * in) - 1;
    }
}

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