Util.java Source code

Introduction

Here is the source code for Util.java

Source

import java.util.Random;

/**
 * BeehiveZ is a business process model and instance management system.
 * Copyright (C) 2011  
 * Institute of Information System and Engineering, School of Software, Tsinghua University,
 * Beijing, China
 *
 * Contact: jintao05@gmail.com 
 *
 * This program is a free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation with the version of 2.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
 */

/**
 * @author Tao Jin
 * 
 */

public class Util {

    // calculate the binomial distribution
    // ret[0] stores the number user given
    // ret[1] stores the count of the corresponding number in ret[0] with the
    // same index
    // for some number, the count maybe 0.
    // the parameter validation must be finished in advance
    public static long[][] getBinomialDistribution(int min, int max, long total) {
        Random rand = new Random(System.currentTimeMillis());
        int n = max - min;
        long[][] ret = new long[2][n + 1];
        int mean = (n + 1) / 2;
        float p = 1;
        if (n > 0) {
            p = (float) mean / (float) n;
        }

        long count = 0;
        for (int i = 0; i <= n; i++) {
            double p_i = combination(n, i) * Math.pow(p, i) * Math.pow((1 - p), (n - i));
            long count_i = (long) (total * p_i);
            ret[0][i] = i + min;
            ret[1][i] = count_i;
            count += count_i;
        }

        while (count < total) {
            int i = rand.nextInt(n + 1);
            ret[1][i]++;
            count++;
        }

        return ret;
    }

    // calculate the combination
    // the value would be very large, so store it in the type of double
    public static double combination(int n, int k) {
        double ret = 1;
        while (k > 0) {
            ret = ret * ((double) n / (double) k);
            k--;
            n--;
        }
        return ret;
    }

}