Julia Set Python

Question

I've trying to make a julia set in python but my output is Nan at some early process. I don't know what causes it. Just for the sake of confession: my programming classes are not good, I don't really know what I am doing, this is mostly from what I've learned from Google.

Here's the code:

import matplotlib.pyplot as plt

c = complex(1.5,-0.6)
xli = []
yli = []
while True:
    z = c
    for i in range(1,101):
        if abs(z) > 2.0:
            break   
        z = z*z + c

    if i>0 and i <100:
        break

xi  = -1.24
xf = 1.4
yi = -2.9
yf = 2.1

#the loop for the julia set 
for k in range(1,51):
    x = xi + k*(xf-xi)/50   
    for n in range(51):
        y = yi + n*(yf-yi)/50
        z = z+ x + y* 1j 
        print z
        for i in range(51):
            z = z*z + c    #the error is coming from somewhere around here
            if abs(z) > 2:  #not sure if this is correct
                xli.append(x)
                yli.append(y)



plt.plot(xli,yli,'bo')
plt.show()      

print xli
print yli

Thank you in advance :)

score 1 · Answer 1 · answered May 04 '16 at 22:12

Just for the sake of confession: I know nothing about Julia sets nor matplotlib.

pyplot seems an odd choice due to its low resolution and the fact that colors can't be specified as a vector alongside X & Y. And had it worked as written, 'bo' would have produced just a grid of blue circles.

Your first while True: loop isn't needed as you've picked what you believe to be a viable c.

Here's my rework of your code:

import matplotlib.pyplot as plt

c = complex(1.5, -0.6)

# image size
img_x = 100
img_y = 100

# drawing area
xi = -1.24
xf = 1.4
yi = -2.9
yf = 2.1

iterations = 8 # maximum iterations allowed (maps to 8 shades of gray)

# the loop for the julia set

results = {}  # pyplot speed optimization to plot all same gray at once

for y in range(img_y):
    zy = y * (yf - yi) / (img_y - 1)  + yi
    for x in range(img_x):
        zx = x * (xf - xi) / (img_x - 1)  + xi
        z = zx + zy * 1j
        for i in range(iterations):
            if abs(z) > 2:
                break
            z = z * z + c
        if i not in results:
            results[i] = [[], []]
        results[i][0].append(x)
        results[i][1].append(y)

for i, (xli, yli) in results.items():
    gray = 1.0 - i / iterations
    plt.plot(xli, yli, '.', color=(gray, gray, gray))

plt.show()

OUTPUT

Julia Set Python

1 Answers1