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SSJ is a Java library for stochastic simulation, developed under the direction of Pierre L'Ecuyer, in the Département d'Informatique et de Recherche Opérationnelle (DIRO), at the Université de Montréal. It provides facilities for generating uniform and nonuniform random variates, computing different measures related to probability distributions, performing goodness-of-fit tests, applying quasi-Monte Carlo methods, collecting (elementary) statistics, and programming discrete-event simulations with both events and processes.

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/*
 * Class:        TruncatedRandomStream
 * Description:  container random stream generating numbers in an interval
                 (a,b) instead of in (0,1)
 * Environment:  Java
 * Software:     SSJ 
 * Copyright (C) 2001  Pierre L'Ecuyer and Université de Montréal
 * Organization: DIRO, Université de Montréal
 * @author       
 * @since

 * SSJ is free software: you can redistribute it and/or modify it under
 * the terms of the GNU General Public License (GPL) as published by the
 * Free Software Foundation, either version 3 of the License, or
 * any later version.

 * SSJ 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.

 * A copy of the GNU General Public License is available at
   GPL licence site.
 */

package umontreal.iro.lecuyer.rng;

import umontreal.iro.lecuyer.rng.RandomStream;


/**
 * Represents a container random stream generating numbers in an interval 
 * (a, b) instead of in (0, 1), where 
 * 0 <= a < b <= 1, 
 * by using the contained stream.
 * If nextDouble returns u for the contained stream,
 * it will return 
 * v = a + (b - a)u, which is uniform over (a, b),
 * for the truncated stream.
 * The method nextInt returns the integer that corresponds to v
 * (by inversion); this integer is no longer uniformly distributed in general.
 * 
 */
public class TruncatedRandomStream implements RandomStream {
   private RandomStream stream;
   private double a;
   private double bminusa;



   public TruncatedRandomStream (RandomStream stream, double a, double b) {
      if (stream == null)
         throw new NullPointerException ("The given stream must not be null");
      if (a >= b)
         throw new IllegalArgumentException ("a must be smaller than b");
      if (a < 0 || b < 0 || a > 1 || b > 1)
         throw new IllegalArgumentException ("a and b must be in [0, 1]");
      this.stream = stream;
      this.a = a;
      bminusa = b - a;
   }

   public void resetStartStream () {
      stream.resetStartStream ();
   }

   public void resetStartSubstream () {
      stream.resetStartSubstream ();
   }

   public void resetNextSubstream () {
      stream.resetNextSubstream ();
   }

   public double nextDouble () {
      double v = stream.nextDouble ();
      return a + v * bminusa;
   }

   public void nextArrayOfDouble (double[] u, int start, int n) {
      stream.nextArrayOfDouble (u, start, n);
      for (int i = start; i < start + n; i++)
         u[i] = a + u[i] * bminusa;
   }

   public int nextInt (int i, int j) {
      return i + (int) (nextDouble () * (j - i + 1));
   }

   public void nextArrayOfInt (int i, int j, int[] u, int start, int n) {
      for (int x = start; x < start + n; x++)
         u[x] = nextInt (i, j);
   }
}