/* 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
*/
// sierpin.c: Creates Sierpinsky gasket fractal 
//  Plot data without connecting datapoints with lines.  

#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 30000                             // number of iterations
#define seed 68111                       // seed for number generator
#define a1 20.0                                           // vertex 1
#define b1 20.0
#define a2 320.0                                          // vertex 2
#define b2 20.0
#define a3 170.0                                          // vertex 3
#define b3 280.0

main() {    
	
  int i;
  double x, y, r;
	
  FILE *output;                           // save data in sierpin.dat
  output= fopen("sierpin.dat","w");
  x = 180.;                                         // starting point
  y = 150.;
  srand48(seed);                             // seed number generator
  for (i = 1 ; i<= max ; i++)   {                 //  draw the gasket
    r = drand48();
    if (r <=  0.3333)  {
      x = 0.5*(x + a1);
      y = 0.5*(y + b1);
    }
    else if (r > 0.3333 && r <=  0.6666) {
      x = 0.5*(x + a2);
      y = 0.5*(y + b2);
    }   
    else {
      x = 0.5*(x + a3);
      y = 0.5*(y + b3);
    }  
    fprintf(output, "%f %f\n", x, y);   
  }
  printf("data stored in sierpin.dat\n");
  fclose(output);
}