Abstract

The following discussions and activities are designed to lead the students to explore the Mandelbrot Set. This lesson is designed as a capstone activity for the idea of fractals started in the Infinity, Self-Similarity and Recursion, Geometric Fractals and Fractals and the Chaos Game lessons. Students are introduced to the notion of a complex number and function iteration in order to motivate the discussion of Julia sets and the Mandelbrot set.

Objectives

Upon completion of this lesson, students will:

• have learned about fractals and built a few
• have investigated Julia sets and the Mandelbrot set
• have been introduced to complex numbers and function iteration

Standards

The activities and discussions in this lesson address the following NCTM standards:

Algebra

Understand patterns, relations, and functions

• represent, analyze, and generalize a variety of patterns with tables, graphs, words, and, when possible, symbolic rules
• relate and compare different forms of representation for a relationship
• identify functions as linear or nonlinear and contrast their properties from tables, graphs, or equations

• develop an initial conceptual understanding of different uses of variables
• use symbolic algebra to represent situations and to solve problems, especially those that involve linear relationships

Specify locations and describe spatial relationships using coordinate geometry and other representational

• use coordinate geometry to represent and examine the properties of geometric shapes

• use visual tools such as networks to represent and solve problems
• recognize and apply geometric ideas and relationships in areas outside the mathematics classroom, such as art, science, and everyday life

Links to other standards.

Student Prerequisites

• Geometric: Students must be able to:
  • recognize basic geometric shapes
• Arithmetic: Students must be able to:
  • work with integers as scale factors and in ratios
  • perform basic operations, including squaring
• Algebraic: Students must be able to:
  • work with simple algebraic expressions and functions, such as linear and quadratic expressions
  • graph ordered pairs of points on the cartesian coordinate plane
• Technological: Students must be able to:
  • perform basic mouse manipulations such as point, click and drag
  • use a browser such as Netscape for experimenting with the activities

Teacher Preparation

Students will need:

• Access to a browser
• Copies of supplemental materials for the activities:
  • function pump worksheet
  • Julia set worksheet
  • Mandelbrot set worksheet

Key Terms

Lesson Outline

This lesson is best implemented with students working individually. Allow the students at least 30 minutes to explore each computer activity.

1. Focus and Review

   Remind students what has been learned in previous lessons that will be pertinent to this lesson and/or have them begin to think about the words and ideas of this lesson:

   • Does anyone remember what a fractal is?
   • What are some fractals that we have looked at thus far?

2. Objectives

   Let the students know what it is they will be doing and learning today. Say something like this:

   • Today, class, we are going to learn to calculate complex number functions and see how these fumctions lead to the creation of fractals such as the Julia set and the Mandelbrot set.
   • We are going to use the computers to learn about complex number functions, but please do not turn your computers on until I ask you to. I want to show you a little about this activity first.

3. Teacher Input
   • Lead a class discussion on two variable functions (which can also be introduced as complex number functions).
   • Lead a class discussion on function iteration and julia sets.

4. Guided Practice
   • Have the students try the computer version of the Function Iterator activity to investigate two-variable function iterations and prisoners and escapees.
   • Have the students try the computer version of the Julia Set activity to investigate what sorts of interesting fractal patterns are possible from the boundaries of prisoner sets.
   • Lead a class discussion on how the Mandelbrot set is built from Julia set behavior.

5. Independent Practice
   • Create a set of patterns for the students to find within the Mandelbrot set.
   • Have the students try the computer version of the Mandelbrot Set activity to investigate what sorts of interesting fractal patterns are possible by zooming in on parts of the set.
6. Closure

   • You may wish to bring the class back together for a discussion of the findings. Once the students have been allowed to share what they found, summarize the results of the lesson.

Alternate Outlines

This lesson can be enhanced in several ways. However, cutting out any of the discussions or activities would limit the student's understanding of the ideas behind the Mandelbrot set.

• Add the additional task of trying to find an image that looks like an actual object.
• Have a contest in which the students are asked to find the most interesting image, with a panel of teachers or the entire class being the judge. (Have the students print out their images so that a display can be set up.)
• If connected to the internet, use the enhanced version of the software, The Fractal Microscope, to explore the Mandelbrot set more fully.

Suggested Follow-Up

After these discussions and activities, the students will have seen how the Mandelbrot set is built for the simple case of quadratic functions. This set has many number-theoretic properties which can be explored. For further reading on this complex and beautiful topic see:

Michael Barnsley, Fractals Everywhere, Academic Press 1988.

Benoit Mandelbrot, The Fractal Geometry of Nature, W. H. Freeman 1982.

H.-O. Peitgen and P. H. Richter, The Beauty of Fractals, Springer-Verlag 1986.