## 28 August 2007

### Indexed

Jessica Hagy's blog Indexed (features a wide variety of quasi-mathematical doodles on index cards. (via Freakonomics. She writes:
This site is a little project that lets me make fun of some things and sense of others. I use it to think a little more relationally without resorting to doing actual math.

Some of the mathematical things she uses:

Venn, or Euler diagrams: this diagram of scary stories told to kids (which include Aesop, the Brothers Grimm, and Leviticus, and her explanation of humor at Freakonomics, among many others (For the record, a Venn diagram specifically allows that all possible intersections of the sets in question and their complements, except for those containing both a set and its complement, are nonempty; an Euler diagram shows the actual intersections and inclusions between sets.

A visual joke about tangents. (This reminds me of a story: I was born at 11:41 in the morning. The first time I learned about Lie algebras, it was my birthday, and I had a lecture that morning to attend from eleven to twelve. I asked a question at about 11:39 or so. My professor went off on a tangent about Lie algebras, and I looked at my watch while he was talking and it was 11:41. I felt all special.)

Correlation does not imply causation. But sometimes correlated things are related by causation: if there's more food around, you get fat.

Optimization problems in music and in food.

Meaningless charts, which I think I've ranted about before.

The same diagrams get recycled with different labels -- for example, this post on money and status, this one on the evils of gym class, and this one on career choice. This is an example of the general phenomenon that lots of apparently different things are governed by the same mathematical structure.

And normal people get laid most following a normal distribution!

The complete graph on six vertices is good for something. Seven vertices, too, but she can't draw a regular heptagon. (Can you?)