/* From: "COMPUTATIONAL PHYSICS, 2nd Ed" 
   by RH Landau, MJ Paez, and CC Bordeianu 
   Copyright Wiley-VCH, 2007.
   Electronic Materials copyright: R Landau, Oregon State Univ, 2007;
   MJ Paez, Univ Antioquia, 2007; & CC Bordeianu, Univ Bucharest, 2007
   Support by National Science Foundation                              
*/                                                                      
// column.c: Correlated ballistic deposition  to form fractalcomment:  

#include <stdio.h>
#include <stdlib.h>

// if you don't have drand48 uncomment the following two lines 
    #define drand48 1.0/RAND_MAX*rand 
    #define srand48 srand                   
      
#define max 100000                            // number of iterations
#define npoints 200                             // no. of open spaces
#define seed 68111                       // seed for number generator
    
main()  {    
	 int i, hit[200], dist, r, x, y, oldx, oldy;
   double  pp, prob;
   FILE *output;
   output = fopen("column.dat","w");        // seed random generator
   srand48(seed);                 
   for (i=0; i<npoints; i++) hit[i] = 0;           // clear the array
   oldx = 100;
   oldy = 0;
   for (i=1; i<=max; i++)  {
     r = (int) (npoints*drand48()); 
     x = r-oldx; 
     y = hit[r]-oldy;
     dist = x*x + y*y;
		 if (dist == 0)  prob = 1.0;           // probability of sticking
      else prob = 9.0/(dist);                       // nu=-2.0, c=0.9
     pp = drand48();
     if (pp < prob)  {
       if ((r>0) && (r<(npoints-1)))  {   
         if ((hit[r] >= hit[r-1]) && (hit[r] >= hit[r+1]))  hit[r]++;
           else if (hit[r-1] > hit[r+1])  hit[r] = hit[r-1];
             else hit[r] = hit[r+1];
       oldx = r;
       oldy = hit[r];
       fprintf(output, "%d\t%d\n", r, hit[r]);  
         }
      }
   }
   printf("data stored in column.dat\n");
   fclose(output);
}