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//******************************************************************************
//
// File: BernoulliPrng.java
// Package: edu.rit.numeric
// Unit: Class edu.rit.numeric.BernoulliPrng
//
// This Java source file is copyright (C) 2011 by Alan Kaminsky. All rights
// reserved. For further information, contact the author, Alan Kaminsky, at
// ark@cs.rit.edu.
//
// This Java source file is part of the Parallel Java Library ("PJ"). PJ 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.
//
// PJ 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.
//
// Linking this library statically or dynamically with other modules is making a
// combined work based on this library. Thus, the terms and conditions of the
// GNU General Public License cover the whole combination.
//
// As a special exception, the copyright holders of this library give you
// permission to link this library with independent modules to produce an
// executable, regardless of the license terms of these independent modules, and
// to copy and distribute the resulting executable under terms of your choice,
// provided that you also meet, for each linked independent module, the terms
// and conditions of the license of that module. An independent module is a
// module which is not derived from or based on this library. If you modify this
// library, you may extend this exception to your version of the library, but
// you are not obligated to do so. If you do not wish to do so, delete this
// exception statement from your version.
//
// A copy of the GNU General Public License is provided in the file gpl.txt. You
// may also obtain a copy of the GNU General Public License on the World Wide
// Web at http://www.gnu.org/licenses/gpl.html.
//
//******************************************************************************
package edu.rit.numeric;
import edu.rit.util.Random;
/**
* Class BernoulliPrng provides a pseudorandom number generator (PRNG) that
* generates random values of type <TT>boolean</TT>. The probability of the
* value true (heads) is <I>p</I>, specified to the constructor. The probability
* of the value false (tails) is <I>q</I> = 1 − <I>p</I>.
*
* @author Alan Kaminsky
* @version 07-Jun-2011
*/
public class BernoulliPrng
{
// Hidden data members.
private final Random myUniformPrng;
private final double myP;
// Exported constructors.
/**
* Construct a new Bernoulli PRNG with heads probability = 0.5.
*
* @param theUniformPrng The underlying uniform PRNG.
*
* @exception NullPointerException
* (unchecked exception) Thrown if <TT>theUniformPrng</TT> is null.
*/
public BernoulliPrng
(Random theUniformPrng)
{
this (theUniformPrng, 0.5);
}
/**
* Construct a new Bernoulli PRNG with the given heads probability.
*
* @param theUniformPrng The underlying uniform PRNG.
* @param p Heads probability, 0 ≤ <I>p</I> ≤ 1.
*
* @exception NullPointerException
* (unchecked exception) Thrown if <TT>theUniformPrng</TT> is null.
* @exception IllegalArgumentException
* (unchecked exception) Thrown if <I>p</I> < 0 or <I>p</I> > 1.
*/
public BernoulliPrng
(Random theUniformPrng,
double p)
{
if (theUniformPrng == null)
{
throw new NullPointerException
("BernoulliPrng(): theUniformPrng is null");
}
if (0.0 > p || p > 1.0)
{
throw new IllegalArgumentException
("BernoulliPrng(): p = "+p+" illegal");
}
myUniformPrng = theUniformPrng;
myP = p;
}
// Exported operations.
/**
* Returns the next random value. True (heads) is returned with probability
* <I>p</I>, false (tails) is returned with probability
* 1 − <I>p</I>.
*
* @return Random value.
*/
public boolean next()
{
return myUniformPrng.nextDouble() < myP;
}
}
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