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The code work in windows system but does not work in linux

  1. Mar 19, 2012 #1
    It looks like dead loop when it is running on linux system.
    It works perfectly in windows.

    Code (Text):

    #include <stdio.h>
    #include <stdlib.h>
    #include <math.h>
    #define NF 10  //total number of data.


    /* function prototypes */

    double gaussian( void );

    int
    main()
    {
        int i;
        double *ave;
       

        srand(2050);
        if(! (ave = malloc( NF * sizeof(double))) )
                printf("memory error \n");

        for(i=0;i<NF;i++)
            ave[i]=gaussian();
        for(i=0;i<NF;i++)
            printf("%e, ", ave[i]);

       
       
    free(ave);


    }



    double
    gaussian( void )
    {
      static int useold = 0;
      static double old;
      if ( useold ) {
        useold = 0;
        return old;
      } else {
        double x, y, r2, norm;
        int j;
        double RAND;
        do {
            j=rand();
            RAND=j*1.0/32767;
          x = 2.0*RAND - 1.0;
          j=rand();
            RAND=j*1.0/32767;
           y = 2.0*RAND - 1.0;
          r2 = x*x + y*y;
        } while ( r2 >= 1.0 || r2 == 0.0 );
        norm = sqrt( -2.0*log( r2 )/r2 );
        old = x*norm;
        useold = 1;
        return y*norm;
      }
    }


     
     
  2. jcsd
  3. Mar 19, 2012 #2

    D H

    User Avatar
    Staff Emeritus
    Science Advisor

    The problem is the way you are using rand(). You are assuming it returns a number between 0 and 32767. Most Linux implementations of rand() return a number between 0 and 2147483647.

    Two solutions:

    #1: You should be dividing by RAND_MAX instead of 32767. On a Linux box, that division by 32767 means your function guassian() will be looping for a long, long, long time.

    #2: Even better, don't not use rand(). It is at best a lousy pseudo random number generator, and in some implementations (e.g., microsoft) it is a very bad pseudo random number generator.
     
  4. Mar 19, 2012 #3
    Thank you very much. I chose the first solution. It's the most easy way~

     
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