RandTool.java

// File: RandTool.java
//
// Author: Rahul Simha
// Created: Feb, 2008
//
// Random generation tools.
// This goes beyond UniformRandom.java in providing additional
// distributions.

import java.util.*;


public class RandTool {

    // Basic Lehmer generator - constants
    static final long m = 2147483647L;
    static final long a = 48271L;
    static final long q = 44488L;
    static final long r = 3399L;
    
    static long r_seed = 12345678L; 
    static Random rand = new Random (r_seed);
    
    public static void setSeed (long seed)
    {
	r_seed = seed;
        rand = new Random (r_seed);
    }
    
    // Basic Lehmer generator - uniform[0,1]
    // For more information see Knuth, Vol. II.
    public static double uniform ()
    {
	long hi = r_seed / q;
	long lo = r_seed - q * hi;
	long t = a * lo - r * hi;
	if (t > 0)
	    r_seed = t;
	else
	    r_seed = t + m;
	return ( (double) r_seed / (double) m );
    }
    
    // U[a,b] generator 
    public static double uniform (double a, double b)
    {
	if (b > a)
	    return ( a + (b-a) * uniform() );
	else { 
	    System.out.println ("ERROR in uniform(double,double):a="+a+",b="+b); 
	    return 0;
	}
    }
    
    // Discrete Uniform random generator - returns an
    // integer between a and b
    public static long uniform (long a, long b)
    {
	if (b > a) {
	    double x = uniform ();
	    long c = ( a + (long) Math.floor((b-a+1)*x) );
	    return c;
	}
	else if (a == b) 
	    return a;
	else { 
	    System.out.println ("ERROR: in uniform(long,long):a="+a+",b="+b); 
	    return 0;
	}
    }
    
    public static int uniform (int a, int b)
    {
	return (int) uniform ((long) a, (long) b);
    }
    
    public static double exponential (double lambda)
    {
        return (1.0 / lambda) * (-Math.log(1.0 - uniform()));
    }

    public static double gaussian ()
    {
        return rand.nextGaussian ();
    }


    public static double gaussian (double mean, double stdDeviation)
    {
        double x = gaussian ();
        return mean + x * stdDeviation;
    }

} // End of class RandTool