code: //==============================================================================
  //	
  //	Copyright (c) 2002-
  //	Authors:
  //	* Dave Parker <david.parker@comlab.ox.ac.uk> (University of Oxford)
  //	* Vincent Nimal <vincent.nimal@comlab.ox.ac.uk> (University of Oxford)
  //	
  //------------------------------------------------------------------------------
  //	
  //	This file is part of PRISM.
  //	
  //	PRISM 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 2 of the License, or
  //	(at your option) any later version.
  //	
  //	PRISM 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 PRISM; if not, write to the Free Software Foundation,
  //	Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
  //	
  //==============================================================================
  
  package simulator;
  
  import java.util.Date;
  
  import cern.jet.random.Exponential;
  import cern.jet.random.Uniform;
  import cern.jet.random.engine.MersenneTwister;
  
  /**
   * Random number generator for the simulator.
   * Currently, uses the Colt library.
   */
  public class RandomNumberGenerator
  {
  	private MersenneTwister random;
  	private Uniform uniform;
  	private Exponential exponential;
  
  	/**
  	 * Create a new random number generator (seeded, by default, with the current time).
  	 */
  	public RandomNumberGenerator()
  	{
  		random = new MersenneTwister(new Date());
  		uniform = new Uniform(random);
  		// Create exponential generator (rate 1.0 but this is ignored from now on)
  		exponential = new Exponential(1.0, random);
  	}
  
  	/**
  	 * Pick a (uniformly distributed) random integer in the range [0,...,n-1].
  	 */
  	public int randomUnifInt(int n)
  	{
  		return uniform.nextIntFromTo(0, n - 1);
  	}
  
  	/**
  	 * Pick a (uniformly distributed) random double in the range (0,1).
  	 */
  	public double randomUnifDouble()
  	{
  		return random.nextDouble();
  	}
  
  	/**
  	 * Pick a (uniformly distributed) random double in range (0,x).
  	 */
  	public double randomUnifDouble(double x)
  	{
  		return x * random.nextDouble();
  	}
  
  	/**
  	 * Pick a random double according to exponential distribution with rate x.
  	 */
  	public double randomExpDouble(double x)
  	{
  		return exponential.nextDouble(x);
  		//return (-Math.log(random.nextDouble())) / x;
  	}
  }
  