Draw the Mandelbrot Set in Python


This tutorial will guide you through a fun project involving complex numbers in Python. You’re going to learn about fractals and create some truly stunning art by drawing the Mandelbrot set using Python’s Matplotlib and Pillow libraries. Along the way, you’ll learn how this famous fractal was discovered, what it represents, and how it relates to other fractals.

Knowing about object-oriented programming principles and recursion will enable you to take full advantage of Python’s expressive syntax to write clean code that reads almost like math formulas. To understand the algorithmic details of making fractals, you should also be comfortable with complex numbers, logarithms, set theory, and iterated functions. But don’t let these prerequisites scare you away, as you’ll be able to follow along and produce the art anyway!

In this tutorial, you’ll learn how to:

Apply complex numbers to a practical problem
Find members of the Mandelbrot and Julia sets
Draw these sets as fractals using Matplotlib and Pillow
Make a colorful artistic representation of the fractals

To download the source code used in this tutorial, click the link below:

Get Source Code: Click here to get the source code you’ll use to draw the Mandelbrot set.

Understanding the Mandelbrot Set

Before you try to draw the fractal, it’ll help to understand what the corresponding Mandelbrot set represents and how to determine its members. If you’re already familiar with the underlying theory, then feel free to skip ahead to the plotting section below.

The Icon of Fractal Geometry

Even if the name is new to you, you might have seen some mesmerizing visualizations of the Mandelbrot set before. It’s a set of complex numbers, whose boundary forms a distinctive and intricate pattern when depicted on the complex plane. That pattern became arguably the most famous fractal, giving birth to fractal geometry in the late 20th century:

Mandelbrot Set (Source: Wikimedia, Created by Wolfgang Beyer, CC BY-SA 3.0)

The discovery of the Mandelbrot set was possible thanks to technological advancement. It’s attributed to a mathematician named Benoît Mandelbrot. He worked at IBM and had access to a computer capable of what was, at the time, demanding number crunching. Today, you can explore fractals in the comfort of your home, using nothing more than Python!

Fractals are infinitely repeating patterns on different scales. While philosophers have argued for centuries about the existence of infinity, fractals do have an analogy in the real world. It’s a fairly common phenomenon occurring in nature. For example, this Romanesco cauliflower is finite but has a self-similar structure because each part of the vegetable looks like the whole, only smaller:

Fractal Structure of a Romanesco Cauliflower

Self-similarity can often be defined mathematically with recursion. The Mandelbrot set isn’t perfectly self-similar as it contains slightly different copies of itself at smaller scales. Nevertheless, it can still be described by a recursive function in the complex domain.

The Boundary of Iterative Stability

Formally, the Mandelbrot set is the set of complex numbers, c, for which an infinite sequence of numbers, z0, z1, …, zn, …, remains bounded. In other words, there is a limit that the magnitude of each complex number in that sequence never exceeds. The Mandelbrot sequence is given by the following recursive formula:

In plain English, to decide whether some complex number, c, belongs to the Mandelbrot set, you must feed that number to the formula above. From now on, the number c will remain constant as you iterate the sequence. The first element of the sequence, z0, is always equal to zero. To calculate the next element, zn+1, you’ll keep squaring the last element, zn, and adding your initial number, c, in a feedback loop.

By observing how the resulting sequence of numbers behaves, you’ll be able to classify your complex number, c, as either a Mandelbrot set member or not. The sequence is infinite, but you must stop calculating its elements at some point. Making that choice is somewhat arbitrary and depends on your accepted level of confidence, as more elements will provide a more accurate ruling on c.

Note: The entire Mandelbrot set fits in a circle with a radius of two when depicted on the complex plane. This is a handy fact that’ll let you skip many unnecessary calculations for points that certainly don’t belong to the set.

With complex numbers, you can imagine this iterative process visually in two dimensions, but you can go ahead and consider only real numbers for the sake of simplicity now. If you were to implement the above equation in Python, then it could look something like this:

>>>>>> def z(n, c):
if n == 0:
return 0
return z(n 1, c) ** 2 + c

Your z() function returns the nth element of the sequence, which is why it expects an element’s index, n, as the first argument. The second argument, c, is a fixed number that you’re testing. This function would keep calling itself infinitely due to recursion. However, to break that chain of recursive calls, a condition checks for the base case with an immediately known solution—zero.

Try using your new function to find the first ten elements of the sequence for c = 1, and see what happens:

Read the full article at https://realpython.com/mandelbrot-set-python/ »

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