cad.simcad.utilz.random
Class MersenneTwister

java.lang.Object
  |
  +--java.util.Random
        |
        +--cad.simcad.utilz.random.MersenneTwister

All Implemented Interfaces:

java.io.Serializable

Direct Known Subclasses:

MTAdapter

public class MersenneTwister

extends java.util.Random

implements java.io.Serializable

Mersenne Twister and MersenneTwisterFast:

MersenneTwister is a drop-in subclass replacement for java.util.Random. It is properly synchronized and can be used in a multithreaded environment.

MersenneTwisterFast is not a subclass of java.util.Random. It has the same public methods as Random does, however, and it is algorithmically identical to MersenneTwister. MersenneTwisterFast has hard-code inlined all of its methods directly, and made all of them final (well, the ones of consequence anyway). Further, these methods are not synchronized, so the same MersenneTwisterFast instance cannot be shared by multiple threads. But all this helps MersenneTwisterFast achieve over twice the speed of MersenneTwister.

About the Mersenne Twister. This is a Java version of the C-program for MT19937: Integer version. next(32) generates one pseudorandom unsigned integer (32bit) which is uniformly distributed among 0 to 2^32-1 for each call. next(int bits) >>>'s by (32-bits) to get a value ranging between 0 and 2^bits-1 long inclusive; hope that's correct. setSeed(seed) set initial values to the working area of 624 words. For setSeed(seed), seed is any 32-bit integer except for 0.

Orignally Coded by Takuji Nishimura, considering the suggestions by Topher Cooper and Marc Rieffel in July-Aug. 1997. More information can be found here.

Translated to Java by Michael Lecuyer January 30, 1999 Copyright (C) 1999 Michael Lecuyer

This library is free software; you can redistribute it and or modify it under the terms of the GNU Library General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version. This library 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 Library General Public License for more details. You should have received a copy of the GNU Library General Public License along with this library; if not, write to the Free Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA

Makoto Matsumoto and Takuji Nishimura, the original authors ask "When you use this, send an email to: matumoto@math.keio.ac.jp with an appropriate reference to your work" You might also point out this was a translation.

Reference. M. Matsumoto and T. Nishimura, "Mersenne Twister: A 623-Dimensionally Equidistributed Uniform Pseudo-Random Number Generator", ACM Transactions on Modeling and Computer Simulation, Vol. 8, No. 1, January 1998, pp 3--30.

About this version. This is a modification of the original code made to conform to proper java.util.Random format by Sean Luke, August 7, 1999.

Bug Fixes. This implementation implements the bug fixes made in Java 1.2's version of Random, which means it can be used with earlier versions of Java. See the JDK 1.2 java.util.Random documentation for further documentation on the random-number generation contracts made. Additionally, there's an undocumented bug in the JDK java.util.Random.nextBytes() method, which this code fixes.

Important Note. Just like java.util.Random, this generator accepts a long seed but doesn't use all of it. java.util.Random uses 48 bits. The Mersenne Twister instead uses 32 bits (int size). So it's best if your seed does not exceed the int range.

See Also:

Serialized Form

Constructor Summary

MersenneTwister()
Constructor using the default seed.

MersenneTwister(long seed)
Constructor using a given seed.

Method Summary

static void	main(java.lang.String[] args) Tests the code.
protected int	next(int bits) Returns an integer with bits bits filled with a random number.
boolean	nextBoolean() This method is missing from jdk 1.0.x and below.
byte	nextByte() For completeness' sake, though it's not in java.util.Random.
void	nextBytes(byte[] bytes) A bug fix for all versions of the JDK.
char	nextChar() For completeness' sake, though it's not in java.util.Random.
double	nextDouble() A bug fix for versions of JDK 1.1 and below.
float	nextFloat() A bug fix for versions of JDK 1.1 and below.
int	nextInt(int n) This method is missing from JDK 1.1 and below.
short	nextShort() For completeness' sake, though it's not in java.util.Random.
void	setSeed(long seed) Initalize the pseudo random number generator.

Methods inherited from class java.util.Random

nextGaussian, nextInt, nextLong

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

MersenneTwister

public MersenneTwister()

Constructor using the default seed.

MersenneTwister

public MersenneTwister(long seed)

Constructor using a given seed. Though you pass this seed in as a long, it's best to make sure it's actually an integer.

Parameters:

seed - generator starting number, often the time of day.

Method Detail

setSeed

public void setSeed(long seed)

Initalize the pseudo random number generator. The Mersenne Twister only uses an integer for its seed; It's best that you don't pass in a long that's bigger than an int. Note that for very old versions of jdk (like 1.0.2), setSeed will not properly reset the gaussian mechanism, so nextGaussian() may return one more extra gaussian drawn from the old seed rather than the new one.

Overrides:

setSeed in class java.util.Random

Parameters:

seed - from constructor

next

protected int next(int bits)

Returns an integer with bits bits filled with a random number.

Overrides:

next in class java.util.Random

nextBoolean

public boolean nextBoolean()

This method is missing from jdk 1.0.x and below. JDK 1.1 includes this for us, but what the heck.

Overrides:

nextBoolean in class java.util.Random

nextInt

public int nextInt(int n)

This method is missing from JDK 1.1 and below. JDK 1.2 includes this for us, but what the heck.

Overrides:

nextInt in class java.util.Random

nextDouble

public double nextDouble()

A bug fix for versions of JDK 1.1 and below. JDK 1.2 fixes this for us, but what the heck.

Overrides:

nextDouble in class java.util.Random

nextFloat

public float nextFloat()

A bug fix for versions of JDK 1.1 and below. JDK 1.2 fixes this for us, but what the heck.

Overrides:

nextFloat in class java.util.Random

nextBytes

public void nextBytes(byte[] bytes)

A bug fix for all versions of the JDK. The JDK appears to use all four bytes in an integer as independent byte values! Totally wrong. I've submitted a bug report.

Overrides:

nextBytes in class java.util.Random

nextChar

public char nextChar()

For completeness' sake, though it's not in java.util.Random.

nextShort

public short nextShort()

For completeness' sake, though it's not in java.util.Random.

nextByte

public byte nextByte()

For completeness' sake, though it's not in java.util.Random.

main

public static void main(java.lang.String[] args)

Tests the code.