Pythagoras tree (fractal)

Construction

The construction of the Pythagoras tree begins with a square. Upon this square are constructed two squares, each scaled down by a linear factor of /2, such that the corners of the squares coincide pairwise. The same procedure is then applied recursively to the two smaller squares, ad infinitum. The illustration below shows the first few iterations in the construction process.

This is the simplest symmetric triangle. Alternatively, the sides of the triangle are recursively equal proportions, leading to the sides being proportional to the square root of the inverse golden ratio, and the areas of the squares being in golden ratio proportion.

Area

Iteration n in the construction adds 2n squares of area \tfrac{1}{2^n}, for a total area of 1. Thus the area of the tree might seem to grow without bound in the limit as n → ∞. However, some of the squares overlap starting at the order 5 iteration, and the tree actually has a finite area because it fits inside a 6×4 box.

It can be shown easily that the area A of the Pythagoras tree must be in the range 5

Varying the angle

An interesting set of variations can be constructed by maintaining an isosceles triangle but changing the base angle (90 degrees for the standard Pythagoras tree). In particular, when the base half-angle is set to (30°) = arcsin(0.5), it is easily seen that the size of the squares remains constant. The first overlap occurs at the fourth iteration. The general pattern produced is the rhombitrihexagonal tiling, an array of hexagons bordered by the constructing squares.

In the limit where the half-angle is 90 degrees, there is obviously no overlap, and the total area is twice the area of the base square.

The Pythagoras tree was first constructed by Albert E. Bosman (1891–1961), a Dutch mathematics teacher, in 1942.

References

References

1. "Bruno's column (0402) Boom van Pythagoras".
2. [http://www.wisfaq.nl/showrecord3.asp?id=32367 Wisfaq.nl].
3. (2011). "Novel Modified Pythagorean Tree Fractal Monopole Antennas for UWB Applications". IEEE.
4. "The Area of the Pythagoras Tree".
5. [http://www.arsetmathesis.nl/bruno0402.htm Arsetmathesis.nl] {{webarchive. link. (2009-01-18)