## 90th Carnival of Mathematics

Welcome to the 90th edition of the Carnival of Mathematics and the first one hosted by me since I handed over the administrative reigns to the good people of aperiodical. The CoM is a great way to read about and promote mathematical blogging and has been running for over 5 years. Hosted on a different blog each month, it covers the entire mathematical spectrum from simple mucking around with numbers right up to cutting edge research.

Writers can submit their own posts for inclusion in a carnival if they like and anyone can submit any mathy post that they’ve found interesting– ideally, something written over the last month or so to keep it fresh.

If you want to keep up with the CoM, head over to its twitter feed or the dedicated page at aperiodical.

**Trivia**

Carnival tradition dictates that I post some trivia about this month’s edition number. Here’s what I came up with for 90:

- 90 is the only number that is the sum of its digits plus the squares of its digits (via NumberGossip)
- 90 is a Harshad number in base 10. It is also a Perrin Number, a pronic number, a unitary perfect number and a semi perfect number.
- 90 is the smallest number that has six representations as a sum of four positive squares (via Wolfram Alpha)

**Neat Stuff**

- Matthew Handy explains how researchers at MIT used geometric series to solve an economic problem in Zeno’s Facebook Page.
- Carnival regular, Pat Ballew tells us about a nice connection between numeric frieze patterns and triangulating polygons.
- Ethan Brown, a thirteen-year-old “Mathemagician” and the author of the blog coolmathstuff.com brings us Probability, The Number e, and Magic all in one

**Computation**

- The Numerical Algorithms Group (NAG) discusses Linear Quantile Regression, a new feature in the latest version of their software.
- Samir Kahn has been Modelling Flow Intertia in Three Couple Liquid Tanks using Maple.
- Cleve Moler, inventor of MATLAB, has written two posts on Conway’s Game of Life (part 1, part 2)

**Puzzles and Games
**

- Shecky R brings us Mind Wrenching – A self-referential logic puzzle that will give your brain cells a workout.
- Brent Yorgey has been visualizing winning strategies for “nim-like” games and says
*‘This is a post about visualizing winning strategies for certain games where players take turns removing counters from two piles. The games make for fun games to actually play, and analyzing them can get quite interesting!’*

**Funnies**

- The xkcd comic shows how pointless the phrase ‘We are the fastest growing [whatever]’ is
- Mark Dominus offers a koan on the Consistency of the Peano Axioms.

**Art and Mathematics
**

- Egan Chernoff sent in Alternative Base Representation saying
*‘I look forward to your critiques of my latest piece’* - Gianluigi Filippelli gives us Poincaré, Einstein and Picasso: children of time and says
*‘Following an article by Arthur I. Miller on the Guardian, I try to tell the possible connections between cubism, mathematics and relativity.’* - Gianluigi continues his cultural theme with a look at some mathematical poems recently published in Nature in The day of mathematical poetry.

**Books**

- Shiva Kintali has reviewed a couple of books – Matching Theory by Laszlo Lovasz and Elements of Automata Theory by Jacques Sakarovitch.

**Tricks and Tactics**

- John D Cook gives us Binomial Coefficient Trick

**Topology**

- Mark Dominus of The Universe of Discourse gives us three posts this month: A two parter on topology and set theory (Click here for part 1 and here for part 2).

**Teaching**

- Dan McQuillan gives us On Trigonometric Nostalgia and says
*‘This is a post about fostering a problem-solving mentality in a world where we do not even understand how our own tools work. It superimposes our nostalgia for the world we used to know with our innate curiosity, which still exists. Basic trigonometry is still fun and still relevant. Indeed, one can always ask questions and calculate!’* - Frederick Koh takes on the dot product in Understanding MATTERS (7) saying ‘T
*his dot product concept involving parallel vector planes is rather fundamental, yet a handful of my students are unable to figure out how things exactly work. Hence I have decided to pen this detailed explanation in the hope that it will benefit not just my charges, but other math learners as well.’* - Augustus Van Dusen has written the first in an upcoming series of posts that will prove properties of logarthmic and exponential functions. Augustus says
*‘This particular post will focus on the properties of logarithmic functions of real variables. Students in advanced placement calculus in high school and beginning college students who are not math majors are the intended audience.’*

**Comment**

- Peter Rowlett asks does mathematics have a culture of historical inaccuracy?
- Mike Thayer submitted his article Tired of playing defense saying
*‘These are my thoughts on the Andrew Hacker NY Times article from July, and the Roger Schank Washington Post article from earlier this week.It is my defense of teaching algebra…’* - Egan Chernoff submits Bill, you had me at “arithmetic” and asks
*‘how do other people feel about the phrase “let’s do the math.” ‘*

**Not the only game in town**

The Carnival of Mathematics isn’t the only mathematical blog carnival that’s doing the tour. There’s also the fantastic monthly Math Teachers at Play.

**End**

That’s it for the 90th Edition. Past editions written by me include 80, 76, 74 and 73 among others. For future editions keep an eye on @carnivalofmath and aperiodical.com