# Xah Math Blog Archive 2012-05

Mathematician Robert J Vanderbei https://www.facebook.com/robert.vanderbei made a comment at Geometry: Gallery of Surfaces. He wrote a surface viewer using latest tech WebGL. It's excellent. Check it out at [ http://www.princeton.edu/~rvdb/WebGL/minsurf.html ] . You will need to use a broweser that supports WebGL, such as Google Chrome.

I can never remember what “xor” do. But now i got a easy way to remember it. xor returns true if the values of two sides differ.

See also: Logical Operators, Truth Table, Unicode

update: Math Font, Unicode, Gothic Letters, Double Struck, 𝔄 𝔅 ℭ

updated links: Great software for Tilings, Patterns, Symmetry

Great Software for Plane Geometry

Understanding Public-Key Cryptography for Beginner

this tweet is going around:

Dear math, i'm sick and tired of finding your x, just accept the fact that she is gone.

It needs a prelude:

dear girls, i had a fight with my x, but i think she loves me still. help me find x^2+1=5. —Math

3 wonderful articles on cycloids. By mathematician physicist John C. Baez .

- Rolling Circles and Balls (Part 1) By John Baez. At http://johncarlosbaez.wordpress.com/2012/08/31/rolling-circles-and-balls-part-1/
- Rolling Circles and Balls (Part 2) By John Baez. At http://johncarlosbaez.wordpress.com/2012/09/03/rolling-balls-and-circles-part-2/
- Rolling Circles and Balls (Part 3) By John Baez. At http://johncarlosbaez.wordpress.com/2012/09/11/rolling-circles-and-balls-part-3/

It mentioned my site a lot. Thanks John.

William Thurston died. (1946 to 2012). Of skin cancer.

I think i first heard of him thru Jeff Week's book 〈The Shapes of Space〉. [see Reading Notes on “The Shape of Space”] I realized that he's one of the world's top mathematician. Though, his work is beyond my understanding.

What Voting Systems are There?

Memories of Kurt Gödel By Rudy Rucker. At http://www.rudyrucker.com/blog/2012/08/01/memories-of-kurt-godel/

### Discovered a Unicode Character ℇ (EULER CONSTANT)

Discovered a Unicode char ℇ

character: ℇ (codepoint 8455, #o20407, #x2107) name: EULER CONSTANT old-name: EULERS

This is a bit strange. It's not clear whether it meant the base of the natural logarithm or Euler–Mascheroni constant .

The symbol for the base of the natural logarithm is traditionally ℯ (SCRIPT SMALL E), while the symbol for Euler–Mascheroni constant is γ (GREEK SMALL LETTER GAMMA).

The Unicode ℇ has name EULER CONSTANT. It's a bit ambiguous, but i suppose it means ℯ. However, i tried several Unicode fonts, all of them has the appearance of mirrored 3, none showed it as ℯ.

Geometric Dissection in Expandable Table Furniture 📺

### Space Groups, Math and Chicks

got a chick from Moscow State University asking me about implementing Space group in Mathematica. Life's been worth living.

- Geometry: Plane Tiling Mathematica Package
- The Discontinuous Groups of Rotation and Translation in the Plane
- Math Tiling Gallery

Anna, yes, you.

… haven't worked on this since 1998. I did 2D version. The 3D version would be much spectacular, especially with today's computing technologies (For example, dynamic rotation in web browser). Also, going into higher dimension (For example, 4th) would be a wonderful exercise in writing combinatorics programs or exploration into proof systems. Dimension 7 or higher hasn't been solved yet. Fame awaits!

Nice article:

- ODE notation considered harmful By ?. At http://stochastix.wordpress.com/2012/06/05/ode-notation-considered-harmful/

See also: The Problems of Traditional Math Notation .

### Fractal Gears

updated: The Problems of Traditional Math Notation

Mandelbrot Set Explained (no complex number needed)

complex number simply explained: Geometric Transformation on the Plane