""" From "A SURVEY OF COMPUTATIONAL PHYSICS", Python eBook Version
   by RH Landau, MJ Paez, and CC Bordeianu
   Copyright Princeton University Press, Princeton, 2012; Book  Copyright R Landau, 
   Oregon State Unv, MJ Paez, Univ Antioquia, C Bordeianu, Univ Bucharest, 2012.
   Support by National Science Foundation , Oregon State Univ, Microsoft Corp"""  

#  Fern.py
from pylab import *
import random

imax = 12000                                            #  points to draw
i = 0
x = 0.5                                                #  initial x coord
y = 0.0                                                #  initial y coord
r = 0.0
xn = 0.0
yn = 0.0

random.seed(899432)                 #  Initialize random number generator
for i in range(1, imax):
    r = random.random();                                 #  random number
    if ( r <=  0.02):                                    # 2% probability
        xn = 0.5
        yn = 0.27*y
    else:
        if ( r > 0.02 and r <=  0.17):                  # 15% probability
            xn =  - 0.139 * x  +  0.263 * y  +  0.57
            yn =  0.246   * x  +  0.224 * y  -  0.036
        else:
            if ( r > 0.17 and r <=  0.3):               # 13% probability
                xn =  0.17 * x  -  0.215 * y  +  0.408
                yn = 0.222 * x  +  0.176 * y  +  0.0893
            else:
                xn = 0.781    * x  + 0.034 * y  + 0.1075     # 70% probab
                yn =  - 0.032 * x  + 0.739 * y  +  0.27
    
    x = xn
    y = yn          
    xc = 2.0 * x - 1.0             #  linear transform 0<x<1  - > - 1<x<1
    yc = 1.8 * y - 1.0             #  linear transform 0<y<1  - > - 1<y<1
    #pts.append(pos=(xc,yc))
#    plot(xc,yc,".",markersize = 1,color = "blue") 
    plot(x,y,".",markersize = 1,color = "blue") 
    draw()

show()