## A Parade of Algorithmic Mathematical Art, by Greg N. Frederickson

A geometric dissection is a cutting of a geometric figure into pieces that we can rearrange to form another figure. Such visual demonstrations of the equivalence of area (or volume) span from the ancient Greeks through current-day postings on the world-wide web. During the past century, the emphasis has been on minimizing the number of pieces for any given dissection, which resulted in some remarkably beautiful mathematical creations. That was the subject of my first book (in 1997).
As dissection methods have become more sophisticated, attention has also focused on special properties, such as having all the pieces of a dissection be connected by hinges. Swing hinges allow the pieces to swing from one figure to the other figure. My second book (2002) surveys swing-hinged dissections, and also introduces twist-hinged dissections. A twist hinge allows one piece to be twisted with respect to another. My third book (2006) explores hinges that allow pieces to be folded one on top of the other.
When giving talks based on my second book, I found it useful to demonstrate actual physical models. I included in my third book a CD containing video clips in which I demonstrated various folding models. That stimulated me to produce computer-generated animations for talks on discoveries made since my third book. Here you will see a parade of animations and video clips that I produced over the last five years. Just as Alexander Calder had his circus, I have my parade!
What makes this art? We see the application of elegant dissection methods to symmetrical figures such as regular polygons and stars. We also see the design of objects such as a table whose top swings from a triangle to a square, and garden benches that twist to ring around a tree. We see individual motions smoothly executed to reveal symmetry and other lovely properties. I still cannot resist watching these animations over and over again.
What makes this algorithmic? Algorithms can be seen both in the creation of smooth motion and in the use of dissection methods on certain infinite families of figures. While perhaps more hidden, hints of the algorithms are detectable if you pay close attention. So relax and enjoy the mesmerizing motion!

### Articles in journals

1. Unexpected twists in geometric dissections,
Graphs and Combinatorics, 23[Suppl] (2007), pp. 245-258.
2. The heptagon to the square, and other wild twists,
Mathematical Intelligencer 29, 4 (2007), pp. 23-33.
3. Designing a table both swinging and stable,
College Mathematics Journal 39, 4 (September 2008), pp. 258-266.
— won the 2009 MAA George Pólya Award.
4. Polishing some visual gems,
Math Horizons , September 2009, pp. 21-25.
5. Casting light on cube dissections,
Mathematics Magazine 82, 5 (December 2009), pp. 323-331.
6. Hugo Hadwiger's influence on geometric dissections with special properties,
Elemente der Mathematik 65, 4 (2010), pp. 154-164.
7. Folding polyominoes from one level to two,
College Mathematics Journal 42, 4 (September 2011), pp. 265-274.

### Papers presented in conferences and workshops

1. Symmetry and structure in twist-hinged dissections of polygonal rings and polygonal anti-rings,
Proc. Bridges Donostia: Mathematics, Music, Art, Architecture, Culture, San Sebastian, Spain (July 2007), pp. 21-28.
2. Dissecting and folding stacked geometric figures,
DIMACS Workshop on Algorithmic Mathematical Art: Special Cases and Their Applications, Rutgers University, Piscataway, NJ (May 11-13, 2009).

### Books

1. Dissections: Plane & Fancy, Cambridge University Press, 1997.
2. Hinged Dissections: Swinging and Twisting, Cambridge University Press, 2002.
3. Piano-hinged Dissections: Time to Fold!, A K Peters Ltd, 2006.