An Interesting Prime Number Fact, Rubik’s Cube and the Gömböc

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Published on: December 29, 2011

In the summer of 2010 I traveled to Hungary for the 25th anniversary reunion of the Budapest Semesters in Mathematics program, and had the pleasure of seeing the inauguration of another study abroad program for computer science, the Aquincum Institute of Technology.

The interesting part of the ceremony was a series of mathematics talks to celebrate the genius of Hungarian mathematics and technology. There were also talks by Balázs Bús, the mayor of Óbuda, and by János Kocsány, the CEO of Graphisoft Park.

The Graphisoft Park Rubik's Cube
The Graphisoft Park Rubik's Cube

László Babai talked about Mathematical Generalizations of Rubik’s Cube, and mentioned the following.

The diameter of the Rubik’s Cube graph is at least 20, but probably no more than 21 (Richard Korf, UCLA, 1997), and definitely no more than 26 (Gene Cooperman, Dan Kunkle, Northeastern, 2007).

It was very interesting that just a month later, in July, 2010, the diameter was confirmed as 20. A team used 35 years of CPU time, donated by Google, to complete the computation. Even more interesting for me was to learn that the lower bound of 20 had been established in 1995 by Mike Reid, who identified the “superflip” position that required 20 moves to solve. Here’s an interesting website that documents progress on this problem: God’s Number is 20.

I had met Mike in person about 25 years ago, when I attended the Hampshire College Summer Studies in Mathematics. Now that I am involved with the New York Math Circle, I’ve had the pleasure of meeting Mike’s old math teachers, who have wonderful stories to tell.

Babai had brought up the diameter of the Rubik’s Cube graph because his talk was really about the connection between the size of a group at the diameter of its Cayley graph. For the Rubik’s cube, the group has about 34 quintillion elements (The exact number is 43,252,003,274,489,856,000. Remember: thousand, million, billion, trillion, quadrillion, quintillion, sextillion, septillion, …), but its diameter is just 20, which is on the order of the logarithm of the size of the group.

Babai mentioned a recent result of Harald Helfgott and Akos Seres, On the diameter of permutation groups, which gives a “quasipolynomial upper bound” for the diameter.

One beautiful formula that Babai presented was:

\prod_{p \leq x} p \approx e^x.

This seems related to the prime number theorem, that \pi(x) \approx \frac{x}{\ln{x}}, where \pi(x) denotes how many primes are less than x. I leave it to the readers to find the connection.

Another great talk was by Gábor Domokos, The Story of Gömböc. The gömböc is a solid object with just one stable point of equilibrium (and also one unstable point). If you place the gömböc on a flat surface, it rocks back and forth, and eventually stabilizes in the same position each time.

Amazing invention–I want one!

Poster Sessions

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Published on: December 28, 2011

After completing a research project or making a mathematical discovery of some sort, it’s important to communicate your results. One nice way to do this is with posters.

If you’ve never made a poster before, it’s simply a collection of boxes that tells a story, in this case, your mathematical research. It should tell a story to someone reading it, but work even better if you’re standing in front of the poster conversing with your audience.

Here are some photos I’ve taken of posters and poster sessions:

There are a lot of useful websites out there about making a poster. Here is one of my favorites:
Creating Effective Poster Presentations :: An Effective Poster

Creativity in Mathematics: Inquiry-Based Learning and the Moore Method

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Published on: December 11, 2011

I just viewed the recent video on the Modified Moore Method (MMO), also known as Inquiry Based Learning (IBL).

Creativity in Mathematics: Inquiry-Based Learning and the Moore Method

This video features interviews with MMO practitioners, researchers and students. I’ve had the pleasure of meeting many of them at various Legacy of R. L. Moore, which have been a lot of fun.

I’ve been developing an approach to IBL in my own teaching, especially in combination with cooperative learning, and have at various times tried to write my own problem sequences. Not an easy task, but very worthwhile!

Project Euler

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Published on: November 28, 2011

My friend Aaron just pointed me to this site, but I think I’d seen it before, in a less-polished state.

Project Euler (http://projecteuler.net/)

This page has a sequence of 360 challenging math and computing problems. If you sign up for an account, you can track your progress in solving the problems. The problems are not trivial at all, so this looks like a great way to challenge yourself and grow both mathematically and in terms of programming.

I’m curious who set up this site. Even more, I think it would be great to work as a team to solve these problems. Add this to my list of fun things to do, if I only had time…

Remembering Mr. Geller

Categories: Math Circle, NYMC
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Published on: November 5, 2011
Richard Geller at Stuyvesant, November 3, 2009
Richard Geller at Stuyvesant, November 3, 2009

I first met Mr. Geller in the mid-80s when I was a high school student. My Stuyvesant math team friends snuck me into the math team practice one morning, and Mr. Geller was the math team coach. Although he enjoyed a reputation for being quite strict, he made an exception in my case and I felt welcome.

When I found myself working in New York starting in 2006, I met Richard again at the New York Math Circle. Richard attended every teachers class, and I pretty much did too.

I took this photo of Richard at Stuyvesant High School just two years ago at the annual math team coaches workshop.  Mr. Geller was there early, and welcomed everyone. I was there to run a middle school math teachers’ circle with the New York Math Circle, and Richard was the one who had invited us in and arranged for the room.

Richard was diagnosed with a melanoma cancer last year, and died on November 1, 2011 at about 1pm. (11/1/11 1pm). He will be missed. In a recent message, his widow, Barbara, wrote that

In lieu of flowers, contributions can be made to a scholarship fund at Stuyvesant High School set up in Richard’s name. Checks can be made out to Richard B Geller Memorial Scholarship for Mathematics and sent to Barbara Geller, 50 West 97th Street #11T, New York, NY 10025.

Here is further reading:

New York Times article: Stuyvesant Students Mourn a Math Teacher Who Was No. 1

The Stuyvesant Spectator article: Richard Geller: The Lifelong Mathematician

Riverside Memorial Chapel: Richard Geller (August 20, 1946 – November 1, 2011)

My Use of Moore Method and IBL

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Published on: October 30, 2011

I just read the following online article: Why Use IBL? and wanted to note the link for later use. This is a great summary of the history, use and effects of Inquiry Based Learning (IBL) in the classroom, and its undergraduate-level cousin, the Modified Moore Method.

My approach to teaching has evolved along with the use of IBL. My work is to develop material to guide my students’ exploration, and then to facilitate their mathematical investigations.

In my current work, I teach two graduate level courses. One is an Abstract Algebra course where I guide my students to reconstruct and understand an unusual proof of the Fundamental Theorem of Algebra first developed by Euler and others. This course is a delightful collection of topics connected by several themes, including problem solving, the connections between graduate level mathematics, use of historical mathematical documents and the school curriculum, and of course, the Fundamental Theorem of Algebra. The other course is a Real Analysis course, which makes use of my modification of Mahavier and Mahavier’s Analysis problem sequence. We don’t have much time, so for this course my personal goal is that the students prove the Intermediate Value Theorem from the ground up.

I liked reading the Why Use IBL? article I mentioned in the first paragraph, so now I intend to make it required reading for my students as they start the Analysis course.

Gathering 4 Gardner

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Published on: October 13, 2011

This year’s G4G, or Gathering for Gardner, Celebration of Mind II, falls on Friday, October 21. This is the second G4G since Martin Gardner passed away on May 22, 2010, and the G4G is intended to celebrate his life and work.

Martin Gardner

You can find a nearby celebration here: http://www.g4g-com.org/

Should you cite Wikipedia?

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Published on: September 29, 2011

The short answer is no, but I think that Wikipedia is an excellent first stop on your way to find better sources.

Move towards the source: Ideally you should cite primary and secondary sources in your work, but Wikipedia might be considered tertiary or even more remote. However, most Wikipedia entries are compiled by knowledgeable human beings who are aware of primary and secondary sources, and prepare excellent reference sections.

Even Wikipedia recommends that you don’t cite them: http://en.wikipedia.org/wiki/Wikipedia:Academic_use

How to Have a Conversation

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Published on: September 24, 2011

One of my favorite sketches in the Monty Python film, The Meaning of Life, is of a middle-aged couple (completely lacking any intellectual curiosity) who have an awkward and scripted conversation.

The waiter tries to interest them in conversations about minorities, football, baseball, and finally manages to start them on a conversation about philosophy.

You can read the conversation here at the movie script site www.intriguing.com.

This sketch came to mind last week when my MAT students and I discussed conversations in class. They told me why they value conversations in math classes, and we considered two math ed articles:

Chazan, D. & Ball, D. L. (1999). Beyond being told not to tellFor the Learning of Mathematics, 9, 2-10.

This article which is based on two case studies, seems to be a reaction against the (then) recently released NCTM Principles and Standards which admonished teachers “not to tell”. Chazan and Ball are eager to describe many classroom circumstances where it is completely appropriate for teachers to take the lead and actively direct the class.

Chazan and Ball leave with three considerations:

Mathematical Value in Relation to Students – does the current student discussion have significant value to the students’ understanding of mathematics? Not all conversations are valuable.

Direction and Momentum – is the conversation at the right pace and level? The waiter in the Monty Python sketch recognized that the couple’s conversation was going nowhere, and helped them get started. The results were, well… let’s say better than before the intervention. A teacher can keep a conversation going at the right pace and at the right level of intellectual challenge for the students.

Social and Emotional Tone – part of the classroom culture is how students treat and respect each other. I’ve seen classes where the students are downright mean to each other, and nobody is willing to take intellectual risks. Luckily, the opposite is true in most classes I visit, and a lot has to do with how the teacher intentionally created the supportive and cooperative atmosphere.

The second article we looked at was more recent, and directed towards teachers taking their first steps at facilitating rich mathematical discussions in class.

Orchestrating Discussions, Margaret S. Smith, Elizabeth K. Hughes, Randi A. Engle, Mary Kay Stein, May 2009, Volume 14, Issue 9, Page 548.

This article presents a framework for teachers in the context of a discussion that follows a student activity on proportional reasoning. The five steps to a successful discussion are:

Anticipating – as part of your planning, imagine different ways that your students could successfully approach the task, and what misconceptions or difficulties they might have. Write these down and have it with you during class.

Monitoring – as you circulate around class during the activity, intentionally monitor your students’ work and identify which students are using the strategies that you’ve anticipated. This frees you up from having to think too much in the moment, since you’re prepared for most of what will happen. It also means that you’ll have more energy to focus things that you have not anticipated.

Selecting – the authors recommend against a show-and-tell style discussion. Instead, carefully select which student work you’d like to highlight, and have a reason to do so.

Sequencing – now that you’ve selected which student work to highlight, the order that the class shares it in is just as important. One possible trajectory is from the simplest strategies to the most abstract, but it’s important to plan a sequence.

Connecting – as the class discusses their solutions, the teacher can make explicit mathematical connections for the students and highlight certain aspects of the material. After the activity, the students are primed for assimilating the new knowledge and connecting it to what they already know, so here is where the teacher can maximize the benefit of the activity.

Favorite Quote

My favorite student comment is that all of this is just plain common sense. That’s how I see it too – that once you’ve read through this article, it’s pretty much self-evident that this is a good way to plan for the discussion after an activity. No controversy here.

Common sense may be a revelation to some, but it might be too often overlooked, and it is useful to hear it once in a while, especially as we get our start in teaching! What is your favorite common sense advice in teaching?

Welcome to the Bard MAT Neighborhood

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Published on: September 24, 2011

One of the many special things about the Bard MAT Program is just how much time students spend out in the schools, allowing for a gentle development of their skills and understandings as teachers.

Now that September is nearing an end, the MAT students will soon scatter around the neighborhood, to the nearby classrooms at some of our partner schools. Here’s a map I made of the placements:


View Welcome to the Bard MAT Neighborhood in a larger map

Where did you do your student teaching? What would make for the ideal student teaching experience?

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Welcome , today is Saturday, January 28, 2012