Xah Math Blog Archive 2016-01

logician Raymond Smullyan is 97 now.

Raymond Smullyan is famous among armature mathematicians for his many books on logic, presented as intriguing logic puzzles.

Knights and Knaves

On a island, all inhabitants are either knights, who always tell the truth, or knaves, who always lie.

John and Bill are residents of the island.

John says: We are both knaves.

Who is what?

here's his books Raymond Smullyan books

Missing square puzzle
Missing square puzzle

Truly Amazing Euler, Greatest Mathematician. A Intro.

truly amazing Euler, greatest mathematician. Here's his story told by William Dunham, 2008. Save 1 hour to watch.

A Tribute to Euler, by William Dunham, 2008. Talk starts at 1:20.
truncated octahedra chc airport 2016-s289x217
Polyhedra Sculptures
Introduction to Graph Theory  Trudeau-s199x314
Graph Theory Book

Adaptive Sampling, Plotting Math Curve

The story of SageMath. http://wstein.org/papers/talks/2016-06-sage-bp/bp.pdf

excellent story, if you want to know about math software, open source, academia.

here's video version.

the origins of SageMath; I am leaving academia to build a company.

Abuse of Math Notation

Why is Mandelbrot Set Cardioid Shaped?

Times Tables, Mandelbrot and the Heart of Mathematics

more about cardioid here: Cardioid

Great Math Puzzles

[The Involute of a Cubical Parabola By John Baez. At https://johncarlosbaez.wordpress.com/2016/03/22/the-involute-of-a-cubical-parabola/ , accessed on 2016-05-14 ]

[The Capricornoid By John Baez. At https://johncarlosbaez.wordpress.com/2016/03/06/the-capricornoid/ , accessed on 2016-05-14 ]

Free Calculus Textbooks

Why Are Text Book So Expensive?

Geometer's Sketchpad Closed Shop? Now, Free Download!

Interactive Geometry of Plane Curves

real rose

Plane Curves: GeoGebra Files Index

update complete. There are 60 of them. Enjoy!

Interactive Geometry of Plane Curves

following are interactive geometry of plane curves.

They are GeoGebra software. Google no longer supports Java Applets. I'm updating them to html5 so they run in your browser. There are about 50 more to do, i'll be posting them in next few days. Hope you like them.

plane tiling mathematica 2016-05-04 35001
Plane Tiling Mathematica package.

been working on Geometry: Plane Tiling Mathematica Package

for illustration at the Nature of Associative Property of Algebra

barth sextic mapped to sphere-s

beautiful images of Barth Sextic

The Symmetries of Things by John H. Conway (Author), Heidi Burgiel (Author), Chaim Goodman-Strauss (Author) Buy at amazon

John H Conway's new old book

math art: islamic pattern metal sphere

cubical two point pattern metal sphere Craig S Kaplan
“cubical two point pattern metal sphere” by Craig S Kaplan. Buy at http://www.shapeways.com/product/Y26YZRL3Y/cubical-two-point-pattern
islamic geometry pattern z
islamic geometry pattern 〈Tending toward the convex〉 [Tending toward the convex By Craig S Kaplan. At http://isohedral.ca/tending-toward-the-convex/ , accessed on 2016-04-04 ]

Craig S Kaplan is a expert at mathematical decorative patterns. You can find more of his work on his site at http://isohedral.ca/

[Computer Generated Islamic Star Patterns By Craig S Kaplan. At http://vismath4.tripod.com/kaplan/index.html ]

visual proofs is such that we have to artfully distribute the errors all over, so that in the limit, the error disappears!

Rectified Truncated Icosahedron and Elongated Square Gyrobicupola

John Baez again, from which i learned about the term “rectification” (of regular polyhedron), and also read what's archimedean solid, and learned about this strange beast Elongated square gyrobicupola .

the Elongated square gyrobicupola is interesting, besides the name, because

It is sometimes considered to be an Archimedean solid, because its faces consist of regular polygons that meet in the same pattern at each of its vertices. However, unlike the rest of the Archimedean solids, it lacks a set of global symmetries that take every vertex to every other vertex.

see Baez's article here: [Rectified Truncated Icosahedron By John Baez. At http://blogs.ams.org/visualinsight/2016/04/01/rectified_truncated_icosahedron/ , accessed on 2016-04-01 ]

by the way, i highly recommend this software KaleidoTile. See Great Math Software: Polyhedrons and Polytopes

Find Intersections of Lines. Bentley–Ottmann Algorithm

In computational geometry, the Bentley–Ottmann algorithm is a sweep line algorithm for listing all crossings in a set of line segments. Wikipedia Bentley–Ottmann algorithm

beautiful internactive demo (JavaScript) by Adam Pearce http://bl.ocks.org/1wheel/464141fe9b940153e636

Prime Number's Ending Digit, Probability

Soundararajan was drawn to study consecutive primes after hearing a lecture at Stanford by the mathematician Tadashi Tokieda, of the University of Cambridge, in which he mentioned a counterintuitive property of coin-tossing: If Alice tosses a coin until she sees a head followed by a tail, and Bob tosses a coin until he sees two heads in a row, then on average, Alice will require four tosses while Bob will require six tosses (try this at home!), even though head-tail and head-head have an equal chance of appearing after two coin tosses.

[Mathematicians Discover Prime Conspiracy. A previously unnoticed property of prime numbers seems to violate a longstanding assumption about how they behave. By Erica Klarreich. At https://www.quantamagazine.org/20160313-mathematicians-discover-prime-conspiracy/ , accessed on 2016-03-15 ]

see also

Free Good Category Theory Book

Mathematician John Baez, and expert of category theory (and quantum mechanics), has a blog about it his course of category theory, at http://math.ucr.edu/home/baez/qg-winter2016/

in particular, he highly recommend this free book on category theory.

Emily Riehl, Category Theory in Context, 2014. Emily_Riehl__Category_Theory_in_Context_2014.pdf

Google AI AlphaGo vs Lee Sedol

Combinatorics, Algorithm, and Humanity

Spare your arithmetic, never count the turns. Once, and a million!

—Shakespeare, in Cymbeline, Act II. Scene IV.

The Three-Body Problem, scifi

black holes and gravitational wave, by Stephen Wolfram


[Black Hole Tech? By Stephen Wolfram. At http://blog.stephenwolfram.com/2016/02/black-hole-tech/ , accessed on 2016-02-23 ]

enjoyed this article. If for nothing, go look at the 3-body problem animation.

classic textbook on algebraic geometry

This is the classic book on algebraic geometry.

Algebraic Geometry Robin Hartshorne cover
[Algebraic Geometry by Robin Hartshorne. Buy at amazon ]

though, i recognized the name. He wrote another book:

Geometry Euclid and Beyond  Robin Hartshorne 0387986502
[Geometry: Euclid and Beyond (Undergraduate Texts in Mathematics) by Robin Hartshorne. Buy at amazon ]

looking at amazon, apparently he wrote a few geometry texts. interesting is that he wrote one on Projective Geometry [Foundations of Projective Geometry Buy at amazon ]

You might find many good geometry texts at Plane Curves Books

… textbooks are too expensive. I think one can find lots of equivalents, cheap or free.

there's something wrong with pricing of textbooks in USA. The price tag is exorbitant. And i think the bottom line cause, is greed. No, am not inclined to blame anything or anyone just because they are successful or rich. But in the case of textbooks, i think indeed it's greed and schemes and made them so expensive, and universities have a lot to do with it.

educational institutions, such as universities, public or privately owned, as big organizations, they are not really doing the good they are supposed to do.

27 Lines on a Cubic Surface

27 Lines on a Cubic Surface – Greg Egan

[27 Lines on a Cubic Surface By John Baez. At http://blogs.ams.org/visualinsight/2016/02/15/27-lines-on-a-cubic-surface/ , accessed on 2016-02-17 ]

Visual Dictionary of Special Plane Curves now has side panel for easy navigation.

Algorithmic Mathematical Art

Google DeepMind AI, AlphaGo to Challenge World Champion?

you may have heard, that Google DeepMind AI, AlphaGo, is doing a human vs machine, challenge a go champion Lee Se-dol.

They said they beat European Champion 5-0, so is now challenging a champion.

I got excited, thought it happened sooner than i expected. Spent some 30 min to read about it. Turns out, that “European champion” is only ranked 2 dan. (Pros are 9 dan)

(go playing is ranked by “dan”, or “level” if you will. Rather a bad system. The chess elo system is much better. But basically, the “dan” is meant to be the number of moves a stronger player can yield to the other for a even game. That is, if you are 4 dan, and i'm 1 dan, that means, if you give me handicap 3 stones (i play 3 moves first, usually on designated spots), then we would have a “even” game. That's the ideal, anyway. In reality, there are professional ranks of dan and armature ranks of dan. Armature 9 dan is something like pro 5 dan.)

so, the AlphaGo human vs machine is rather marketing deception. Am very disappointed and annoyed by the marketing tactics.

this “news”, is rather no news. The go human champion would beat google's AI 5-0.

Ladybug Video Game, Optimal Strategy