Carnival of Mathematics #65

May 7, 2010

Consider two numbers i,j with no common factors, and take the sum of their squares i^2+j^2:

In many cases the result is a prime, twice a prime, a prime power, or twice a prime power . Consider the others, shown in red. We have  65 = 1^2 +8^2 = 4^2 +7^2, 85=2^2+9^2=6^2+7^2, 130=9^2+7^2 and 145=8^2+9^2. Expanding our search however we can also find that 130 = 11^3+3^2 and 145=12^2+1^2. All numbers in this table that do not have the forms described therefore also occur more than once in the table. In fact every number that can be represented in exactly one way as the sum of two squares is a prime, twice a prime, a prime power, or twice a prime power . This makes 1 an idoneal number, suitable number or ideoneal number. More generally this is a number D such that any number that has a unique representation as i^2+D j^2 (where i^2 and D j^2 are coprime) is the now familiar list: a prime, a prime power, or twice a prime power.  These numbers were studied by Euler who said:

An outstanding paradox stands upon this, for although the idoneal numbers are shaped and proceed according to a certain law, the multitude of which however are not infinite yet are extended even onto 65 terms, concern- ing this paradox I have recorded so far no more of this type in the succession which has been observed; yet neither on the other hand has it been permit- ted by me to make firm a finite number of terms, except that after the 65th term, which is 1848, none thereafter have been bestowed, even though I have continued the examination up to 10000 and beyond.

So it brings me great pleasure to announce the 65th maths carnival.

From Euler there is only one place to go, the debate over who are the greatest mathematicians. There were a couple of posts on this topic. Euler made it into a post by Alex Bellos justifying his selections for a previous top ten article in the Times. Tanya Khovanova, however did leave Euler out, but this was understandable, she was looking at living mathematicians. To keep debate rumbling, I will add my top five favourite mathematicians. The ones whose work has most inspired me personally. In historical order they are, Archimedes, Gottfried Leibniz, Felix Klein, John Conway and Tim Gowers.

Having started with a little pure mathematics, the rest of this carnival focuses on the links between mathematics and other things.

Art and Circles

One of my favourite links is of course mathematics and art and that is well represented. The wonderful Math Monday post on the Make blog, showed how to whittle knots and links, and several others played with images from parts of circles, spirographs and a circle puzzle. If you prefer to sit back and just watch GrrlScientist on Living the Scientific Life shows a beatiful maths and nature movie, that has gone viral, though it does have a little too much of the over-hyped golden ratio.

Logic and Computer Programs

One of the darks arts of programming is the creation of Quines, programs that can output their own source code (without cheating). Metaspring develop this idea to show how it can be extended to form the heart of the deep results of Kurt Gödel.  Computers are also of use for more practical things, but to do this we often need to make approximations, for example of the normal distribution.  Code can also provide elegant ways to construct mathematical objects, such as a collection of algorithms to make a matrix with a single 1.

Maps and Calculation

Before computers a whole world of charts to do calculation were developed. Dead Reckonings shows the example of Lallemand’s Hexagonal charts helping ships to determine precise directions from a magnetic compass. Modern mathematics can also help us think about how to navigate our world. Dave Richeson in Division by zero, uses the similarity between topological and topographic to explore this.

You would not expect…

The favourite line of the maths evangelist is that “maths is everywhere”, I am not sure if I go that far, but it certainly turns up in some unusual places. Just a mon looks at the mathematics of the premier league. Even a chiropractor can find uses for mathematics, though lets hope it is use, not abuse, like the BCA’s famous take on the British legal system.

Education

All links between mathematics and other things require people who can understand and apply the mathematical ideas. The great Terrance Tao gives some ideas on games that help you develop this mathematical thinking. From Let’s Play Math, you can even have a bit of fun with calculus.

Elections

To finish on a topical note, I was writing this carnival as I watched the British election. With the hung parilament and the discussions now going on the electoral system itself is coming under question. What does a mathematician think of this? Tim Gowers has some interesting comments.


Mathematical materials

July 20, 2009

To start with a little housekeeping. I have rather neglected this blog, as the summer science exhibition rather took it out of me.  I am also going to retire the unscheduled post tag. It was initially more for links and small things, but twitter is a better medium for that than a blog, so follow me (@gelada) if you want. I am also going to stop attempting the weekly posting. I will put out things when I have them, hopefully not too infrequently.

In order to give a little back this post is a collection of mathematics books and materials that might be of interest. It will also be going on the website for the exhibit.  On the subject of that website it now has pdfs of all the posters and factsheets from the exhibit. They are all licenced under a share-alike licence so you can use them as you wish, as long as you make what you do available in turn.

Now for the page of materials that will be published first here (but a matter of minutes, but here!).

Books:

Popular:

All the authors listed here have several books worth investigating. Here I suggest one each, but there is plenty more to explore!

The Mathematical Tourist

I have to lead off with the book that introduced me to the Penrose tiling. A wander through various mathematical topics, from string theory to chaos. Its a little long in the tooth now, originally published in 1988 and with a second edition 10 years later, but still wonderful writing.

Annotated Flatland: A Romance of Many Dimensions

From a old book to an older one. Flatland is a satire of Victorian society set in a 2d world. Thinking about how the 2d inhabitants consider 3d, can help understand the mysteries of 4d. This edition with modern mathematical commentry from Ian Stewart. There is also now Flatland – The Movie with Martin Sheen!

Professor Stewart’s Cabinet of Mathematical Curiosities

Ian Stewart (mentioned above) has for many years been the star of British poplular mathematics. Along with the Mathematical Tourist his books made me want to become a mathematician. This book from last year is a fascinating collection from all over mathematics.

Finding Moonshine: A Mathematician’s Journey Through Symmetry

If Ian Stewart has been the star, Marcus Du Sautoy is now giving serious competition, getting “The Story of Maths” on television and having a, sadly ended, column in the Times on “Sexy Maths”. In this book he takes ideas about symmetry that come directly from simple questions about shapes and shows how they have been taken to incredible deep mathematics.

Jews in Hyperspace

Just as Flatland was originally a political book, satirising society as much as it describes mathematics, prolific maths and science writer Clifford Pickover mixes a plea for religious harmony with a trip into four dimensions. For his more standard writings on mathematics check out The Math Book

Mathematics: A Very Short Introduction

As you can see from above mathematics has been well served by creative mathematicians writing about their subject. Even so this book is special, Tim Gowers is a winner of the Fields medal, the mathematical Nobel prize. He is also known for the simplicity and expository nature of his work. You could not therefore ask for a better account of what mathematics is, from one of its modern masters.

The Colossal Book of Mathematics

Martin Gardner generated a huge amount of popular mathematics content and is probably responsible for bringing more people to mathematics than anyone else alive. Amongst many other achievements he was the first to publish the Penrose tilings in his Scientific American article. This book brings together a broad collection of his work.

Fermat’s Last Theorem

To finish, no list like this could be complete without mentioning Simon Singh’s masterpiece on the fascinating historical and mathematical story of Fermat’s Last theorem. A note in a margin that lead to a 350 year quest, finally solved by Andrew Wiles in 1995.

More mathematical

For the more ambitious who want to look at the mathematics in more detail, here are some more books.

The Symmetries of Things

This book is probably the most relevant to the exhibition. With over 1000 pictures it also takes a similar visual approach to the mathematics. It is written in a very approachable style and takes the mathematics of symmetry from first principles through to modern research. In fact beyond the images the final section of the book is primarily of interest to researchers, and contains work that pushes forward the cutting edge in this field.

Indra’s Pearls: The Vision of Felix Klein

Another maths book stuffed full of great pictures. This treads a different path to the generalisation of geometry that started with the genius of Felix Klein in the nineteenth century. More recently, thanks to computers, we can actually explore some stunning images that come out of these beautiful mathematical ideas.

Tilings and Patterns

This has been a bible on tilings since it was published, and after several years being hard to find it will be reissued by Dover this winter. Though some sections of it have been put a little out of date by Symmetries of Things it is still a beautiful very visual book with masses of details to dig through.

The Princeton Companion to Mathematics

For the very ambitious this pulls no punches, attempting to cover the whole of modern mathematics in a way accessible to anyone with A-level mathematics. By its own admission it does not make this goal, but it does cover most of the big ideas in an incredibly accessible way.

Materials:

As well as reading you might want to follow up the exhibit with more practical activities. There are wonderful toys available for this. Firstly I should mention the wonderful Polydron and Zometool who sponsored our exhibit. You will have seen their products on display!

Other toys, posters and so on are available from Tessellations, Tarquin books and Grand Illusions.

Finally the Institute of Figuring has a mission to enhance public understanding of figures and models that has a big intersection with mathematics. They are perhaps most famous for the hyperbolic coral reef, based on the hyperbolic crochet patterns of Daina Taimina and we saw a couple of beautiful examples brought along to the exhibit.

Podcasts:

To conclude if you would rather sit back and listen there are some great podcasts on mathematics available.

Mathfactor

Mathematical puzzles, interviews and explanations, from Chaim Goodman-Strauss in Arkansas.

Travels in a mathematical world

Peter Rowlett of the IMA travels round Britain for his job as university liason officer. On the way he interviews many of the people he meets.


WoW 7: The secret life of numbers

May 14, 2009

Numbers are one hell of a powerful idea, and some idea of them seems to predate a lot of other intelligence traits. Even young chicks have some ability to count. (this story was a great reverse April fool, true even though it hit the news on April the first). With the internet we can see for the first time how numbers get used. The secret lives of numbers is a fascinating visualisation of this data, though it is getting a little long in the tooth. Maybe its time to automate this and take weekly accounts from google, giving a detailed history of numbers as well as direct comparison.

Frequencies of the first million numbers

Frequencies of the first million numbers

Maxwell Demon: Website of the week

I am handing out awards, the imaginatively titled “Maxwell’s Demon” website of the week:

wowThere is even a prize, £50.  Though I am lazy so the conditions of this are that the winner:

1) Realises they have won.

2) Contacts me.

3) Puts the logo on their site.

Of course 3 is hard to enforce so you could probably take the money and remove the graphical mess.  I will therefore claim that 3 is to ensure that you are indeed the winner.


WoW 6: Gorgeous 4d graphics

May 6, 2009

At some point I should write something about 4d polytopes. They are an incredible work of the human imagination. There are a few places you can find good information on them, just google them.  Or go to the wikipedia page.  If you do the latter you will find some wonderful images.  You might wonder how they were made.  I did, and was very happy for it. Some of them come from an open source application: jenn3d

The still images it produces are beautiful out of the box:

Bi-truncated 8-cell

Bi-truncated 8-cell

Truncated 24-cell

Truncated 24-cell

The great thing is it is open source so you can go in and hack at it to make your own images, it also has a slightly unclear command line format to specify models.

Tetrahedra from truncated 120-cell

Tetrahedra from truncated 120-cell

Maxwell Demon: Website of the week

I am handing out awards, the imaginatively titled “Maxwell’s Demon” website of the week:

wowThere is even a prize, £50.  Though I am lazy so the conditions of this are that the winner:

1) Realises they have won.

2) Contacts me.

3) Puts the logo on their site.

Of course 3 is hard to enforce so you could probably take the money and remove the graphical mess.  I will therefore claim that 3 is to ensure that you are indeed the winner.


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