randomgenerator.java

一个很好的LIBSVM的JAVA源码。对于要研究和改进SVM算法的学者。可以参考。来自数据挖掘工具YALE工具包。

/*
 *  YALE - Yet Another Learning Environment
 *  Copyright (C) 2001-2004
 *      Simon Fischer, Ralf Klinkenberg, Ingo Mierswa, 
 *          Katharina Morik, Oliver Ritthoff
 *      Artificial Intelligence Unit
 *      Computer Science Department
 *      University of Dortmund
 *      44221 Dortmund,  Germany
 *  email: [e-mail]
 *  web:   http://yale.cs.uni-dortmund.de/
 *
 *  This program 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 2 of the
 *  License, or (at your option) any later version. 
 *
 *  This program 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.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program; if not, write to the Free Software
 *  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307
 *  USA.
 */
package edu.udo.cs.yale.tools;

import edu.udo.cs.yale.Yale;
import edu.udo.cs.yale.Experiment;
import edu.udo.cs.yale.tools.ParameterService;

import java.util.Random;

/** The global random number generator. This should be used for all random purposes of Yale to ensure that two runs of 
 *  the same experiment provide the same results. 
 *
 *  @author ralf, ingo
 *  @version $Id: RandomGenerator.java,v 2.8 2004/09/04 20:07:04 ingomierswa Exp $
 */
public class  RandomGenerator extends Random {

    /** Use this alphabet for random String creation. */
    private static final String ALPHABET = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";

    /** Global random number generator using the random number generator seed specified
     *  for the root operator (ExperimentOperator). */
    private static RandomGenerator globalRandomGenerator;

    /** The seed of this random generator. */
    private long seed;

    /** Initializes the random number generator with the given <code>seed</code> */
    public  RandomGenerator(long seed) {
	super(seed);
	this.seed = seed;
    }


    // ================================================================================

    /** Returns the global random number generator. */
    public static RandomGenerator getGlobalRandomGenerator() {  return globalRandomGenerator;  }

    /** Instantiates the global random number generator and initializes it with the 
     *  random number generator seed specified in the <code>global</code> section of
     *  the configuration file. Should be invoked before the experiment starts. */
    public static void init(Experiment experiment) {
	long seed = experiment.getRootOperator().getParameterAsInt("random_seed");
	globalRandomGenerator = new RandomGenerator(seed);
    }

    /** Returns the random seed for YALE. */
    public long getSeed() {
	return seed;
    }

    // ================================================================================


    /** Returns the next pseudorandom, uniformly distributed <code>double</code> value between 
     *  <code>lowerBound</code> and <code>upperBound</code> from this random number
     *  generator's sequence (exclusive of the interval endpoint values).
     */
    public double nextDoubleInRange(double lowerBound, double upperBound) {
	if (upperBound <= lowerBound) {
	    throw new IllegalArgumentException("RandomGenerator.nextDoubleInRange : the upper bound of the " +
					       "random number range should be greater than the lower bound.");
	}
	return ((nextDouble() * (upperBound - lowerBound)) + lowerBound);
    }

    /** returns the next pseudorandom, uniformly distributed <code>long</code> value between 
     *  <code>lowerBound</code> and <code>upperBound</code> from this random number
     *  generator's sequence (exclusive of the interval endpoint values).
     */
    public long nextLongInRange(long lowerBound, long upperBound) {
	if (upperBound <= lowerBound) {
	    throw new IllegalArgumentException("RandomGenerator.nextLongInRange : the upper bound of the " +
					       "random number range should be greater than the lower bound.");
	}
	return ((long)(nextDouble() * ((double)(upperBound - lowerBound + 1))) + lowerBound);
    }

    /** Returns the next pseudorandom, uniformly distributed <code>int</code> value between 
     *  <code>lowerBound</code> and <code>upperBound</code> from this random number
     *  generator's sequence (exclusive of the interval endpoint values). */
    public int nextIntInRange(int lowerBound, int upperBound) {
	if (upperBound <= lowerBound) {
	    throw new IllegalArgumentException("RandomGenerator.nextIntInRange : the upper bound of the " +
					       "random number range should be greater than the lower bound.");
	}
	return ((int)(nextDouble() * ((double)(upperBound - lowerBound + 1))) + lowerBound);
    }

    /** Returns a random String of the given length. */
    public String nextString(int length) {
	char[] chars = new char[length];
	for (int i = 0; i < chars.length; i++)
	    chars[i] = ALPHABET.charAt(nextInt(ALPHABET.length()));
	return new String(chars);
    }

    /** Returns a randomly selected integer between 0 and the length of the given array.
     *  Uses the given probabilities to determine the index, all values in this array must sum up to 1. */
    public static int randomIndex(double[] probs) {
	double r = globalRandomGenerator.nextDouble();
	double sum = 0.0d;
	for (int i = 0; i < probs.length; i++) {
	    sum += probs[i];
	    if (r < sum) return i; 
	}
	return probs.length-1;
    }
}