# Monthly Archives: September 2019

# Dilating the Delta

A circle with a radius of one unit has an area of exactly π units = 3.141592… units. An equilateral triangle inscribed in the unit circle has an area of 1.2990381… units, or 41.34% of the area of the unit circle.

In other words, triangles are cramped! And so it’s often difficult to see what’s going on in a triangle. Here’s one example, a fractal that starts by finding the centre of the equilateral triangle:

Triangular fractal stage #1

Next, use that central point to create three more triangles:

Triangular fractal stage #2

And then use the centres of each new triangle to create three more triangles (for a total of nine triangles):

Triangular fractal stage #3

And so on, trebling the number of triangles at each stage:

Triangular fractal stage #4

Triangular fractal stage #5

As you can see, the triangles quickly become very crowded. So do the central points when you stop drawing the triangles:

Triangular fractal stage #6

Triangular fractal stage #7

Triangular fractal stage #8

Triangular fractal stage #9

Triangular fractal stage #10

Triangular fractal stage #11

Triangular fractal stage #12

Triangular fractal stage #13

Triangular fractal (animated)

The cramping inside a triangle is why I decided to dilate the delta like this:

Triangular fractal

↓

Circular fractal from triangular fractal

Triangular fractal to circular fractal (animated)

Formation of the circular fractal (animated)

And how do you dilate the delta, or convert an equilateral triangle into a circle? You use elementary trigonometry to expand the perimeter of the triangle so that it lies on the perimeter of the unit circle. The vertices of the triangle don’t move, because they already lie on the perimeter of the circle, but every other point,

*p*, on the perimeter of the triangles moves outward by a fixed amount,

*m*, depending on the angle it makes with the center of the triangle.

Once you have *m*, you can move outward every point, *p*(1..i), that lies between *p* on the perimeter and the centre of the triangle. At least, that’s the theory between the dilation of the delta. In practice, all you need is a point, (*x*,*y*), inside the triangle. From that, you can find the angle, θ, and distance, *d*, from the centre, calculate *m*, and move (*x*,*y*) to *d* * *m* from the centre.

You can apply this technique to any fractal created in an equilateral triangle. For example, here’s the famous Sierpiński triangle in its standard form as a delta, then as a dilated delta or circle:

Sierpiński triangle

↓

Sierpiński triangle to circular Sierpiński fractal

Sierpiński triangle to circle (animated)

But why stop at triangles? You can use the same elementary trigonometry to convert any regular polygon into a circle. A square inscribed in a unit circle has an area of 2 units, or 63.66% of the area of the unit circle, so it too is cramped by comparison with the circle. Here’s a square fractal that I’ve often posted before:

Square fractal, jump = 1/2, ban on jumping towards any vertex twice in a row

It’s created by banning a randomly jumping point from moving twice in a row 1/2 of the distance towards the same vertex of the square. When you dilate the fractal, it looks like this:

Circular fractal from square fractal, *j* = 1/2, ban on jumping towards vertex *v*(i) twice in a row

Circular fractal from square (animated)

And here’s a related fractal where the randomly jumping point can’t jump towards the vertex directly clockwise from the vertex it’s previously jumped towards (so it can jump towards the same vertex twice or more):

Square fractal, *j* = 1/2, ban on vertex *v*(i+1)

When the fractal is dilated, it looks like this:

Circular fractal from square, *i* = 1

Circular fractal from square (animated)

In this square fractal, the randomly jumping point can’t jump towards the vertex directly opposite the vertex it’s previously jumped towards:

Square fractal, ban on vertex *v*(i+2)

And here is the dilated version:

Circular fractal from square, *i* = 2

Circular fractal from square (animated)

And there are a lot more fractals where those came from. Infinitely many, in fact.

# Purple Poesy

DIVERSIONS OF THE RE-ECHO CLUB

It is with pleasure that we announce our ability to offer to the public the papers of the Re-Echo Club. This club, somewhat after the order of the Echo Club, late of Boston, takes pleasure in trying to better what is done. On the occasion of the meeting of which the following gems of poesy are the result, the several members of the club engaged to write up the well-known tradition of the Purple Cow in more elaborate form than the quatrain made famous by Mr. Gelett Burgess:

“I NEVER saw a Purple Cow,

I never hope to see one;

But I can tell you, anyhow,

I’d rather see than be one.”

[…]

MR. A. SWINBURNE:

Oh, Cow of rare rapturous vision,

Oh, purple, impalpable Cow,

Do you browse in a Dream Field Elysian,

Are you purpling pleasantly now?

By the side of wan waves do you languish?

Or in the lithe lush of the grove?

While vainly I search in my anguish,

Bovine of mauve!

Despair in my bosom is sighing,

Hope’s star has sunk sadly to rest;

Though cows of rare sorts I am buying,

Not one breathes a balm to my breast.

Oh, rapturous rose-crowned occasion

When I such a glory might see!

But a cow of a purple persuasion

I never would be.

Elsewhere other-engageable:

• The Purple Cow Parodies

• Diversions of the Re-Echo Club

• *Such Nonsense! An Anthology* (c. 1918) — with this and other parodies