/*  From: "COMPUTATIONAL PHYSICS, 2nd Ed" 
c  by RH Landau, MJ Paez, and CC Bordeianu 
c  Copyright Wiley-VCH, 2007.
c  Electronic Materials copyright: R Landau, Oregon State Univ, 2007;
c  MJ Paez, Univ Antioquia, 2007; and CC Bordeianu, Univ Bucharest, 2007.
c  Support by National Science Foundation                                                                               
*/
//  int10d.c: Ten dimensional Monte-Carlo integration     

#include <stdio.h>
#include <stdlib.h>
#include <math.h>
// if you don't have drand48 uncomment the following two lines 
    #define drand48 1.0/RAND_MAX*rand 
    #define srand48 srand                     
#define max 65536                                 // number of trials

main()  {
	
   int i,j;
   double n = 1.0,x,y = 0; 
   FILE *output;                          // save data in int_10d.dat
   output= fopen("int_10d.dat", "w"); 
   for (i = 1; i<= max; i++)  {
		                                                       // reset x
     x = 0;                  
		                                            // sum of 10 x values
     for (j = 1; j<= 10; j++) x+= drand48();      
       y+= x*x;                                        
			                                         // save after 2, 4, 8,
       if (i%(int)(pow(2.0,n)) == 0) {    
          n++;
          fprintf( output, "%i\t\t%f\n", i, y/i);
      }     
   }
printf("data saved in int_10d.dat\n");       
fclose(output);
}