physis.core.random
Class MersenneTwister

java.lang.Object
  |
  +--physis.core.random.Randomness
        |
        +--physis.core.random.MersenneTwister

public class MersenneTwister

extends Randomness

Mersenne Twister

This work is based on version MT199937 (99/10/29) of the Mersenne Twister algorithm found at * The Mersenne Twister Home Page.

About the Mersenne Twister

This is a Java version of the C-program for MT19937: Integer version. The MT19937 algorithm was created by Makoto Matsumoto and Takuji Nishimura, who ask: "When you use this, send an email to: matumoto@math.keio.ac.jp with an appropriate reference to your work". Indicate that this is a translation of their algorithm into Java.

Reference. Makato Matsumoto and Takuji 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 version of the code implements the MT19937 Mersenne Twister algorithm, with the 99/10/29 seeding mechanism. The original mechanism did not permit 0 as a seed, and odd numbers were not good seed choices. The new version permits any 32-bit signed integer. This algorithm is identical to the MT19937 integer algorithm; real values conform to Sun's float and double random number generator standards rather than attempting to implement the half-open or full-open MT19937-1 and MT199937-2 algorithms.

Changes Since V3: Slight modification to the coin flip algorithms ensures that 0.0 and 1.0 probabilities always return false and true.

The MersenneTwister code is based on standard MT19937 C/C++ code by Takuji Nishimura, with suggestions from Topher Cooper and Marc Rieffel, July 1997. The code was originally translated into Java by Michael Lecuyer, January 1999, and is Copyright (c) 1999 by Michael Lecuyer. The included license is as follows:

The basic algorithmic work of this library (appearing in nextInt() and setSeed()) 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

Important Note on Seeds

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.

Field Summary

private static long	DEFAULT_SEED
private static int	LOWER_MASK
private static int	M
private int[]	mag01
private static int	MATRIX_A
private int[]	mt
private int	mti
private static int	N
private static int	TEMPERING_MASK_B
private static int	TEMPERING_MASK_C
private static int	UPPER_MASK

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.
int	next(int bits) Returns an integer with bits bits filled with a random number.
void	setSeed(long seed) Initalize the pseudo random number generator.
void	setSeedOld(long seed) Initalize the pseudo random number generator.

Methods inherited from class physis.core.random.Randomness

nextBoolean, nextBoolean, nextByte, nextBytes, nextDouble, nextFloat, nextInt, nextInt, nextLong, raw

Methods inherited from class java.lang.Object

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

Field Detail

N

private static final int N

M

private static final int M

MATRIX_A

private static final int MATRIX_A

UPPER_MASK

private static final int UPPER_MASK

LOWER_MASK

private static final int LOWER_MASK

TEMPERING_MASK_B

private static final int TEMPERING_MASK_B

TEMPERING_MASK_C

private static final int TEMPERING_MASK_C

mt

private int[] mt

mti

private int mti

mag01

private int[] mag01

DEFAULT_SEED

private static final long DEFAULT_SEED

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.

Method Detail

setSeedOld

public void setSeedOld(long seed)

Initalize the pseudo random number generator. This is the old seed-setting mechanism for the original Mersenne Twister algorithm. You must not use 0 as your seed, and don't pass in a long that's bigger than an int (Mersenne Twister only uses the first 32 bits for its seed). Also it's suggested that for you avoid even-numbered seeds in this older seed-generation procedure.

setSeed

public final void setSeed(long seed)

Initalize the pseudo random number generator. Don't pass in a long that's bigger than an int (Mersenne Twister only uses the first 32 bits for its seed).

next

public final int next(int bits)

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

Overrides:

next in class Randomness

main

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

Tests the code.