001/*
002 * RandomExponentialDistribution.java
003 * Copyright (c) 2002 
004 *
005 * This program is free software; you can redistribute it and/or
006 * modify it under the terms of the GNU General Public License
007 * as published by the Free Software Foundation; either version 2
008 * of the License, or any later version.
009 *
010 * This program is distributed in the hope that it will be useful,
011 * but WITHOUT ANY WARRANTY; without even the implied warranty of
012 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
013 * GNU General Public License for more details.
014 *
015 * You should have received a copy of the GNU General Public License
016 * along with this program; if not, write to the Free Software
017 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
018 */
019
020
021package ca.bc.webarts.widgets.random;
022
023import java.util.Random;
024
025/**
026 *
027 * A generator of random numbers with exponential distribution.
028 *
029 * (C) 2000, Laurentiu Cristofor (laur72_98@yahoo.com)
030 *
031 **/
032public class RandomExponentialDistribution
033{
034  private Random rand;
035  private double mean;
036
037  /**
038   * Create a new generator of random numbers
039   * with exponential distribution of mean 1.
040   */
041  public RandomExponentialDistribution()
042  {
043    this(1.0);
044  }
045
046  /**
047   * Create a new generator of random numbers
048   * with exponential distribution of specified mean.
049   *
050   * @param mean   the mean of the exponential distribution
051   */
052  public RandomExponentialDistribution(double mean)
053  {
054    this.mean = mean;
055    rand = new Random();
056  }
057
058  /**
059   * Return a random number with exponential distribution.
060   */
061  public double nextDouble()
062  {
063    double val;
064
065    do
066      val = rand.nextDouble();
067    while (val == 0.0);
068
069    return mean * (-Math.log(val));
070  }
071
072  public static void main(String[] args)
073  {
074    RandomExponentialDistribution exponential 
075      = new RandomExponentialDistribution();
076
077    for (int i = 0; i <= 10; i++)
078      System.out.println(exponential.nextDouble());
079  }
080}
081
082