fi.smaa.libror.RandomUtil.java Source code

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Here is the source code for fi.smaa.libror.RandomUtil.java

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/*
 * This file is part of libror.
 * libror is distributed from http://smaa.fi/libror
 * Copyright (C) 2011-15 Tommi Tervonen.
 *
 * This program is 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, either version 3 of the License, or
 * (at your option) any later version.
 *
 * 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, see <http://www.gnu.org/licenses/>.
 */

package fi.smaa.libror;

import java.util.Arrays;

import org.apache.commons.math.random.MersenneTwister;

public class RandomUtil {

    private static MersenneTwister random = new MersenneTwister(0x667);

    /**
     * Generates a sample from uniform distribution in interval [0.0, 1.0].
     * 
     * @return the sampled number
     */
    public static double createUnif01() {
        return random.nextDouble();
    }

    /**
     * Creates an array of random numbers that sum to a given amount.
     * 
     * @param dest the array to create the numbers to.
     * @param sumTo The amount the numbers must sum to. Must be >= 0.0
     * @throws NullPointerException if dest == null
     */
    public static void createSumToRand(double[] dest, double sumTo) throws NullPointerException {
        if (sumTo < 0.0) {
            throw new IllegalArgumentException("sumTo negative");
        }
        if (dest == null) {
            throw new NullPointerException("destination array null");
        }

        int len = dest.length;
        for (int i = 0; i < len - 1; i++) {
            dest[i] = createUnif01() * sumTo;
        }

        dest[len - 1] = sumTo;

        Arrays.sort(dest);

        double last = 0.0;
        for (int i = 0; i < len; i++) {
            double t = dest[i];
            dest[i] = t - last;
            last = t;
        }
    }

    /**
     * Creates random numbers that sum to 1.0.
     * 
     * @param dest the destination array to create the random numbers to
     * @throws NullPointerException if dest == null
     */
    public static void createSumToOneRand(double[] dest) throws NullPointerException {
        createSumToRand(dest, 1.0);
    }

    /**
     * Creates random numbers that sum to 1.0 and are sorted in ascending order.
     * 
     * @param dest the destination array to create the random numbers to
     * @throws NullPointerException if dest == null
     */
    public static void createSumToOneSorted(double[] dest) throws NullPointerException {
        createSumToOneRand(dest);
        Arrays.sort(dest);
    }

    public static void createSorted(double[] dest) {
        for (int i = 0; i < dest.length; i++) {
            dest[i] = createUnif01();
        }
        Arrays.sort(dest);
    }
}