Package pal.math

Class MersenneTwisterFast

  • All Implemented Interfaces:
    java.io.Serializable

    public class MersenneTwisterFast
    extends java.lang.Object
    implements java.io.Serializable
    MersenneTwisterFast: A simulation quality fast random number generator (MT19937) with the same public methods as java.util.Random.

    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.

    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.

    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.

    Sean Luke's web page

    - added shuffling method (Alexei Drummond)

    See Also:
    Serialized Form
    • Constructor Summary

      Constructors 
      Constructor Description
      MersenneTwisterFast()
      Constructor using the time of day as default seed.
      MersenneTwisterFast​(long seed)
      Constructor using a given seed.
    • Method Summary

      All Methods Static Methods Instance Methods Concrete Methods 
      Modifier and Type Method Description
      static boolean getNextBoolean()
      Access a default instance of this class, access is synchronized
      static byte getNextByte()
      Access a default instance of this class, access is synchronized
      static void getNextBytes​(byte[] bs)
      Access a default instance of this class, access is synchronized
      static char getNextChar()
      Access a default instance of this class, access is synchronized
      static double getNextDouble()
      Access a default instance of this class, access is synchronized
      static float getNextFloat()
      Access a default instance of this class, access is synchronized
      static int getNextInt()
      Access a default instance of this class, access is synchronized
      static long getNextLong()
      Access a default instance of this class, access is synchronized
      static short getNextShort()
      Access a default instance of this class, access is synchronized
      boolean nextBoolean()  
      byte nextByte()  
      void nextBytes​(byte[] bytes)  
      char nextChar()  
      double nextDouble()  
      float nextFloat()  
      double nextGaussian()  
      int nextInt()  
      int nextInt​(int n)
      Returns an integer drawn uniformly from 0 to n-1.
      long nextLong()  
      short nextShort()  
      void setSeed​(long seed)
      Initalize the pseudo random number generator.
      void shuffle​(int[] array)
      Shuffles an array.
      void shuffle​(int[] array, int numberOfShuffles)
      Shuffles an array by repeatedly choosing two random members and swapping them.
      void shuffle​(java.lang.Object[] array)
      Shuffles an array of objects.
      int[] shuffled​(int l)
      Generates an array of ints that are shuffled
      void shuffleSubset​(int startIndex, int length, java.lang.Object[] array)
      Shuffles an array of objects.
      • Methods inherited from class java.lang.Object

        clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
    • Constructor Detail

      • MersenneTwisterFast

        public MersenneTwisterFast()
        Constructor using the time of day as default seed.
      • MersenneTwisterFast

        public MersenneTwisterFast​(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

      • shuffle

        public final void shuffle​(int[] array)
        Shuffles an array.
        Parameters:
        array - The array of ints to shuffle
      • shuffleSubset

        public final void shuffleSubset​(int startIndex,
                                        int length,
                                        java.lang.Object[] array)
        Shuffles an array of objects.
        Parameters:
        array - The array of objects to shuffle
        startIndex - the starting index of the portion of the array to shuffle
        length - the length of the portion of the array to shuffle
      • shuffle

        public final void shuffle​(java.lang.Object[] array)
        Shuffles an array of objects.
        Parameters:
        array - The array of objects to shuffle
      • shuffle

        public final void shuffle​(int[] array,
                                  int numberOfShuffles)
        Shuffles an array by repeatedly choosing two random members and swapping them.
        Parameters:
        numberOfShuffles - The number of times to do the random swap operation
        array - The array of ints to shuffle
      • shuffled

        public int[] shuffled​(int l)
        Generates an array of ints that are shuffled
        Parameters:
        l - length of the array required.
        Returns:
        an array of shuffled indices of the specified length.
      • setSeed

        public final 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.
        Parameters:
        seed - from constructor
      • nextInt

        public final int nextInt()
      • nextShort

        public final short nextShort()
      • nextChar

        public final char nextChar()
      • nextBoolean

        public final boolean nextBoolean()
      • nextByte

        public final byte nextByte()
      • nextBytes

        public final void nextBytes​(byte[] bytes)
      • nextLong

        public final long nextLong()
      • nextDouble

        public final double nextDouble()
      • nextGaussian

        public final double nextGaussian()
      • nextFloat

        public final float nextFloat()
      • nextInt

        public int nextInt​(int n)
        Returns an integer drawn uniformly from 0 to n-1. Suffice it to say, n must be > 0, or an IllegalArgumentException is raised.
      • getNextByte

        public static final byte getNextByte()
        Access a default instance of this class, access is synchronized
      • getNextBoolean

        public static final boolean getNextBoolean()
        Access a default instance of this class, access is synchronized
      • getNextBytes

        public static final void getNextBytes​(byte[] bs)
        Access a default instance of this class, access is synchronized
      • getNextChar

        public static final char getNextChar()
        Access a default instance of this class, access is synchronized
      • getNextDouble

        public static final double getNextDouble()
        Access a default instance of this class, access is synchronized
      • getNextFloat

        public static final float getNextFloat()
        Access a default instance of this class, access is synchronized
      • getNextLong

        public static final long getNextLong()
        Access a default instance of this class, access is synchronized
      • getNextShort

        public static final short getNextShort()
        Access a default instance of this class, access is synchronized
      • getNextInt

        public static final int getNextInt()
        Access a default instance of this class, access is synchronized