# Xah Math Blog Archive 2010-11 to 2010-12

Math Politics: Simon Plouffe and nth Digit Formula of π

What's Function, What's Operator? (exposition)

Logical Operators, Truth Table, Unicode (thoughts; tutorial)

Added more symbols to Emacs: xah-math-input.el.

∅ ƒ Ø ⌘ ⌥ ‸ ⇞ ⇟ ↖ ↘ ⌫ ⌦ ⎋ ⏏ ↶ ↷ ⇧ ⌤ ⇄ ⇤ ⇥ ↹ ↵ ↩ ⏎ ⌧ ⌨ ␣ ⌶ ⎗ ⎘ ⎙ ⌚ ⌛ ✂ ✄ ✉ ✍ □ ○ ◇ ■ ● ◆.

The symbol “ƒ” has Unicode name “LATIN SMALL LETTER F WITH HOOK”, and its old Unicode name is “LATIN SMALL LETTER SCRIPT F”.

It's a popular symbol on the mac in the 1990s. Often, a folder's name will end with it. You can type it on the Mac by pressing 【`⌥ option`+`f`】 See: Mac OS Roman.
In math, that symbol is sometimes used to stand for “function”.

Many other symbols above are computer key symbols. They are used by Apple. (See: Short Survey of Keyboard Shortcut Notations)

◀ ▶ ▲ ▼ ◁ ▷ △ ▽ ☉ ☼ ☾ ☽ ☿ ♁ ♄ ♅ ♆ ♇ ♃ ♂ ♀ ☄

The symbols includes the 9 planets. Note that in Unicode the ♂ (unicode name MALE SIGN) and ♀ (FEMALE SIGN) is the same symbol for Mars and Venus. Unicode does not have separate char for them.

Also some interesting readings. See: Astronomical symbol.

Also, discovered this article about the pseudo-science book Worlds in Collision, which was a best-seller in 1950s. But today's people probably all forgot about it. By analogy, you should know that many concepts, ideas, practices, we have today in math, sciences, in programing, are probably garbage. In particular, i could personal say this is so with regards to math notations, computer syntaxes, and many computing practices (For example, Design Patterns, eXtreme Programing, which were hot in early 2000s but today pretty much waned. See: Why Software Suck) See also: Men Are From Mars, Women Are From Venus.

Also added the del operator Nabla symbol ∇. The partial derivative symbol ∂.

If you use Emacs and type a lot math symbols, you may be happy to note that i wrote tool for inputting math symbols. See: Emacs: xah-math-input.el.

For why i created it, see: Design of Math Symbols Input System

Math Font, Unicode, Gothic Letters, Double Struck.

Discovered another citation to my Wallpaper groups: The 17 Wallpaper Groups work.

Chapter 1 Symmetry Groups Mathematics in Art and Architecture GEK1518 Helmer Aslaksen Department of Mathematics National University of Singapore aslaksen@math.nus.edu.sg www.math.nus.edu.sg/aslaksen/ Symmetry and Patterns

At Source www.math.nus.edu.sg.

More links:

- Trochoids: Curves Generated by a Rolling Circle By Christopher J Henrich. At http://userpages.monmouth.com/~chenrich/Trochoids/Trochoids.html. Links to:Visual Dictionary of Special Plane Curves.
- Home page of Davide Alessandro Reduzzi (Math 33A, lec. 3 to Linear Algebra and Applications) By Davide Alessandro Reduzzi. At http://www.math.ucla.edu/~devredu83/. Links to Conic Sections

See also: XahLee.org Site Awards and Recognition.

How Mathematica does Unicode? (tutorial)

Tools to Display Math on Web (tips)

some links to xahlee.org math:

- MATH 741: Spectral geometry of random metrics By Dmitry Jakobson. McGill University. Source www.math.mcgill.ca. Links to Visual Dictionary of Special Plane Curves.
- Math 214 - Differential Manifolds, Fall 2010 By Jonathan Dahl. UC Berkeley. Source math.berkeley.edu. Links to Gallery of Famous Surfaces
- Supplements to some chapters of Experiencing Geometry By David W Henderson. Cornell University. math.cornell.edu. Links to Inversion.

Plants vs Zombie; Thoughts on Strategy and Game Formulation

Principia Mathematica (random thoughts)

It's my greatest sorrow to have found that my friend Robby Villegas has died last month. Robby Villegas Died.

Math Typesetting, Mathematica, MathML (random thoughts)

See: Mathematica Logos thru its History.

Criticisms on Criticisms on a New Kind of Science

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