beta分布 java代码

public class BetaDistributionActivity {    /**     * @param alpha: eg. click     * @param beta : eg. pv - click     */

public static double BetaDist(double alpha, double beta) {        double a = alpha + beta;        double b = Math.sqrt((a - 2) / (2 * alpha * beta - a));        if (Math.min(alpha, beta) <= 1) {            b = Math.max(1 / alpha, 1 / beta);        }        double c = alpha + 1 / b;        double W = 0;        boolean reject = true;        while (reject) {            double U1 = Math.random();            double U2 = Math.random();            double V = b * Math.log(U1 / (1 - U1));            W = alpha * Math.exp(V);            reject = (a * Math.log(a / (beta + W)) + c * V - Math.log(4)) < Math.log(U1 * U1 * U2);        }        return (W / (beta + W));    }

}