graycodecounter.java

金融资产定价,随机过程,MONTE CARLO 模拟 JAVA 程序和文档资料

/* WARANTY NOTICE AND COPYRIGHT
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.

Copyright (C) Michael J. Meyer

[e-mail]
[e-mail]

*/


/*
 * Gray.java
 *
 * Created on May 23, 2002, 2:51 PM
 */

package Examples.QuasiMonteCarlo;

/** <p>Prints the grey codes gray(n), n=1,2,...,299 computed both directly and 
 *  recursivley by changing (XORing with 1) the relevant bit.
 *  Done to see how irregularly the grey counter runs through the integers.</p>
 *
 * <p>Recall that we use gray code counting to move through the integers in
 * our implementations of low discrepancy sequences based on base b=2.</p>
 *
 * @author  Michael J. Meyer
 */
public class GrayCodeCounter {
    
    
    /** Print binary string representation of a positive integer n.
     *  Most significant digit leftmost as usual.
     */
    public static void printbin(int n)
    {
        if(n>0)
        { printbin(n/2); System.out.print(n%2); }
    }
    
    // position j of the rightmost zero bit in n, counting starts from zero
    public static int thebit(int n)
    {
        int j=0;
        while(n%2==1){ n=n>>1; j++; }
        
        return j;
    }
    
    public static int twopower(int j)
    {
        int m=1;
        for(int i=0;i<j;i++)m*=2;
        return m;
    }
    
    
    /** The Gray code of n.
     */
    public static int gray(int n){ return n^(n/2); }
    
    
    public static void main(String[] args)
    {
        int n=1, m=1;
        
        
        while(n<257){
            
            // grey code directly and recursive by changing the bit
            System.out.print(gray(n)+", "+m+"\n");
            int j=thebit(n);
            m=m^(1<<j);
          
            n++;
        }
       

    } // end main
    
}