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RandomNumbersTool.java

/* $RCSfile$
 * $Author: egonw $
 * $Date: 2007-01-11 12:46:09 +0100 (Thu, 11 Jan 2007) $
 * $Revision: 7690 $
 * 
 * Copyright (C) 1997-2007  The Chemistry Development Kit (CDK) project
 * 
 * Contact: cdk-devel@lists.sourceforge.net
 * 
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public License
 * as published by the Free Software Foundation; either version 2.1
 * of the License, or (at your option) any later version.
 * All we ask is that proper credit is given for our work, which includes
 * - but is not limited to - adding the above copyright notice to the beginning
 * of your source code files, and to any copyright notice that you may distribute
 * with programs based on this work.
 * 
 * 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 Lesser General Public License for more details.
 * 
 * You should have received a copy of the GNU Lesser General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 */
package org.openscience.cdk.math;

import java.util.Random;

/**
 * Class supplying useful methods to generate random numbers.
 * This class isn't supposed to be instantiated. You should use it by calling
 * its static methods.
 * 
 * @cdk.module  standard
 */
00039 public class RandomNumbersTool extends Random {
    
    private static final long serialVersionUID = -8238833473383641882L;
    
    private static java.util.Random random;
    private static long randomSeed;

    static {
        randomSeed=System.currentTimeMillis();
        random=new java.util.Random(randomSeed);
    }

    /**
     * Sets the base generator to be used by this class.
     * <p>
     * @param base_random a <code>java.util.Random</code> subclass.
     */
00056     public static void setRandom(java.util.Random base_random)
    {
        random=base_random;
    }

    /**
     * Sets the seed of this random number generator using a single
     * <code>long</code> seed.
     *
     * @param new_seed  the seed to be used by the random number generator.
     */
00067     public static void setRandomSeed(long new_seed)
    {
        randomSeed=new_seed;
        random.setSeed(randomSeed);
    }

    /**
     * Returns the seed being used by this random number generator.
     * <p>
     * @return the <code>long</code> seed.
     */
00078     public static long getRandomSeed()
    {
        return randomSeed;
    }

    /**
     * Generates a random integer between <code>0</code> and <code>1</code>.
     * <p>
     * @return a random integer between <code>0</code> and <code>1</code>.
     */
00088     public static int randomInt()
    {
        return randomInt(0,1);
    }

    /**
     * Generates a random integer between the specified values.
     * <p>
     * @param lo the lower bound for the generated integer.
     * @param hi the upper bound for the generated integer.
     * @return a random integer between <code>lo</code> and <code>hi</code>.
     */
00100     public static int randomInt(int lo,int hi)
    {
        return (Math.abs(random.nextInt())%(hi-lo+1))+lo;
    }

    /**
     * Generates a random long between <code>0</code> and <code>1</code>.
     * <p>
     * @return a random long between <code>0</code> and <code>1</code>.
     */
00110     public static long randomLong()
    {
        return randomLong(0,1);
    }

    /**
     * Generates a random long between the specified values.
     * <p>
     * @param lo the lower bound for the generated long.
     * @param hi the upper bound for the generated long.
     * @return a random long between <code>lo</code> and <code>hi</code>.
     */
00122     public static long randomLong(long lo,long hi)
    {
        return (Math.abs(random.nextLong())%(hi-lo+1))+lo;
    }

    /**
     * Generates a random float between <code>0</code> and <code>1</code>.
     * <p>
     * @return a random float between <code>0</code> and <code>1</code>.
     */
00132     public static float randomFloat()
    {
        return random.nextFloat();
    }

    /**
     * Generates a random float between the specified values.
     * <p>
     * @param lo the lower bound for the generated float.
     * @param hi the upper bound for the generated float.
     * @return a random float between <code>lo</code> and <code>hi</code>.
     */
00144     public static float randomFloat(float lo,float hi)
    {
        return (hi-lo)*random.nextFloat()+lo;
    }

    /**
     * Generates a random double between <code>0</code> and <code>1</code>.
     * <p>
     * @return a random double between <code>0</code> and <code>1</code>.
     */
00154     public static double randomDouble()
    {
        return random.nextDouble();
    }

    /**
     * Generates a random double between the specified values.
     * <p>
     * @param lo the lower bound for the generated double.
     * @param hi the upper bound for the generated double.
     * @return a random double between <code>lo</code> and <code>hi</code>.
     */
00166     public static double randomDouble(double lo,double hi)
    {
        return (hi-lo)*random.nextDouble()+lo;
    }

    /**
     * Generates a random boolean.
     * <p>
     * @return a random boolean.
     */
00176     public static boolean randomBoolean()
    {
        return (randomInt()==1);
    }

    /**
     * Generates a random bit: either <code>0</code> or <code>1</code>.
     * <p>
     * @return a random bit.
     */
00186     public static int randomBit()
    {
        return randomInt();
    }

    /**
     * Returns a boolean value based on a biased coin toss.
     * <p>
     * @param p the probability of success.
     * @return <code>true</code> if a success was found; <code>false</code>
     * otherwise.
     */
00198     public static boolean flipCoin(double p)
    {
        return (randomDouble()<p ? true : false);
    }

    /**
     * Generates a random float from a Gaussian distribution with the specified
     * deviation.
     * <p>
     * @param dev the desired deviation.
     * @return a random float from a Gaussian distribution with deviation
     * <code>dev</code>.
     */
00211     public static float gaussianFloat(float dev)
    {
        return (float)random.nextGaussian()*dev;
    }

    /**
     * Generates a random double from a Gaussian distribution with the specified
     * deviation.
     * <p>
     * @param dev the desired deviation.
     * @return a random double from a Gaussian distribution with deviation
     * <code>dev</code>.
     */
00224     public static double gaussianDouble(double dev)
    {
        return random.nextGaussian()*dev;
    }

    /**
     * Generates a random float from an Exponential distribution with the specified
     * mean value.
     * <p>
     * @param mean the desired mean value.
     * @return a random float from an Exponential distribution with mean value
     * <code>mean</code>.
     */
00237     public static float exponentialFloat(float mean)
    {
        return (float)(-mean*Math.log(randomDouble()));
    }

    /**
     * Generates a random double from an Exponential distribution with the specified
     * mean value.
     * <p>
     * @param mean the desired mean value.
     * @return a random double from an Exponential distribution with mean value
     * <code>mean</code>.
     */
00250     public static double exponentialDouble(double mean)
    {
        return -mean*Math.log(randomDouble());
    }
}


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