As of May 4 2007 the scripts will autodetect your timezone settings. Nothing here has to be changed, but there are a few things

## Saturday, November 30, 2013

### Organizing Research Notes

If only Mindjet's MindManager could handle LaTeX it would be the perfect tool for organizing my notes, unfortunately it can't and their advice is to use stuff like Equation Editor. That's not for me.

Perhaps at a subconscious level I find that the notes I produce aren't worth saving, fact is that I still haven't found a way of organizing my study notes that suits me. I regularly search the web for tools and today I landed on this MathOverflow question. From this page I jumped to Dror Bar-Natan's Academic Pensieve, which I invite you to visit because it's unique, impressive and might give you some ideas in organizing your own set of study ( or raw research ) notes.

I have tried a Zillion mindmappers but none come close to MindManager. At work I use FreePlane because it is free (  ( That accurately describes my position with that company ) , the alternative would be to struggle with the tools provided like the damned Word. FreePlane does support LaTeX however.

My little search this morning landed me on DocEar. It supposedly is the MindMapper for Scientists, while MindManager is more positioned at creative business people.  If it is any good, I will report on it in a future post.

UPDATE:
I am giving DocEar a try. It's based on FreePlane and JabRef tools that have proved themselves. More later.

## Sunday, November 24, 2013

### Open University: TMA Cut-off date

As an OU student you have to make several TMAs for each course you do. TMA stands for Tutor Marked Assignment. A TMA consists of assignments covering all the booklets you studied in the period prior to the cut-off date of the TMA. The cut-off date is the latest date the work has to be received by your Tutor. This is a period of cut-off dates. Usually you'll find a lot of blog, forum, twitter or facebook posts about TMAs that have been done. Completing a TMA is just part of the study process but for an OU student it's somewhat of an event. Not like an exam, but sending it out gives a feeling of relief, achievement perhaps. Completing a TMA is not something most people do in a few hours, some TMAs take weeks if not months to complete.

The average result of the TMA ( after some formula has been applied to it ), is the maximum result you can get from the course because the final result of the course is the minimum of the exam result and the average TMA score. Also, a minimum TMA score is required to be eligible for taking the exam. For example.
TMA result: 15/100 not eligible for exam.
TMA result: 65/100. Exam result: 100/100. Course result 65/100.
TMA result: 100/100. Exam result: 15/100. Course result 15/100 and thus a FAIL.
Completing all the TMAs on time, requires regular study, and regular study enhances the chance on a good exam result significantly. I suppose that's the thought behind it all. The second example may seem rather undesirable, but it just is not a realistic scenario. A student with a 100% exam score usually has no problems with the TMAs.

Personally, the TMAs are no longer my 'major math challenge'. Slowly but steady I am working on my own mathematical projects. I still need to study, of course, but I am an OU student mainly to justify the time I spend on mathematics to the other stakeholders in my time. - When you say you study mathematics as a hobby, people accept it ( at best ), but explaining that, in fact, you are involved in your own mathematical research is worse than telling that you apply the tools of Scientology in your life. So... I am an OU Student, if you know what I mean. ;-)

### Closed PolyLine - (2)

I developed an algorithm that takes sequences like $\{ 6, 2, 4, 3, 3, 2, 4, 2, 3, 2, 3, 3, 4, 4, 3, 3, 4 \}$ and turns them into drawings like this ( in Mathematica, of course ).

In order to determine if the tile above tiles the plane I need to remove all internal lines...

... which turned out a tad more dificult than expected. I got as far as a prototype algorithm which I am currently testing and improving.

To be continued.

## Sunday, November 17, 2013

### Closed PolyLine

The picture ( below) contains two drawings ( created with Mathematica ), the drawing on the left consists of a hexagon, a square, a triangle and again a square. In order to facilitate an algorithm that decides if this drawing tiles the plane I need a closed polyline to determine if a point is within the borders of the drawing. Oddly enough it is more difficult to create the drawing on the right than the original on the left.

The drawing on the right is a closed polyline, it consists of a number (11) of line segments and has no begin- and endpoint, it is closed. ( In another project I am working on we call PolyLines, MultiLines but I haven't seen that name in use elsewhere. )

### Geometric cell division

Take a square and add a similar square to one of its sides and remove the shared edge. What remains is a rectangle.

Take an octagon and add a similar octagon to one of its sides and remove the shared edge. What remains is the following polygon.

Take an n-gon and add a similar n-gon to one of its sides and remove the shared edge. At infinity the n-gons will divide into two circles. Unfortunately my computer is too slow to effectively record this in a video.
 n=12

 n=32

 n=64

## Saturday, November 9, 2013

### Example of a polygonal tiling

The tiling in the image below is edge-to-edge, polygonal, but not uniform because it has different vertex types, i.e. (3,3,4,3,4), (3,4,4,6), (3,4,6,4) and (3,6,4,4). It is therefore NOT an Archimedean tiling,

With the following piece we can tile the entire plane...

... as we can see here.

### Regular polygons, exercise.

With a drawing program yesterday's pictures are easy to fake, of course. But these drawing programs don't give you the numbers.

Exercise.

Place a decagon edge-to-edge on a square with sides of length 1 ( see figure ). What is the distance between the two marked points?

( Answer: $\frac{1}{4} \left(3 \sqrt{10-2 \sqrt{5}}+\sqrt{50-10 \sqrt{5}}+4\right)$ )

## Friday, November 8, 2013

### Printing polygons edge-to-edge

Recipe
Suppose you have some polygon with cornerpoints { p1, p2, ..., pk } and you want to print a regular polygon with n edges along one of its edges (p(j), p(j+1) then you can simply find the first point of the regular n-gon by rotating p(j+1) with centre p(j) over 360/n degrees. You can continue this process until you have found all points or you can calculate the centre of the regular polygon, its orientation and edge-length which you need to print a regular n-gon. Here are some examples.

Examples
 3-on-4, 4-on-3 and and 5,7,9,11-on 4 (dark-on-light ).

### The (3,12,12) Tiling

I made ( what programmers would call ) a 'recipe' for creating a program that prints an Archimedean Tiling. Needless to say that I am talking about Mathematica code. I basically have a program that can distribute any set of Mathematica Graphics objects over a lattice of points. So the recipe basically means calculating the points of the motif, putting them in a set and handing them over to the printer. The last one I did is (3,12,12) Tiling.
 Tiling with vertex type (3,12,12).
The next step is to abstract and code the recipe itself, i.e. translating lists like (3,12,12) or (3,3,4,3,4) to graphics. In fact, I calculated the points for (3,12,12) with a first version of that program. -

## Tuesday, November 5, 2013

### Johannes Kepler and (3,3,4,3,4)

Who doesn't know the name of Johannes Kepler? Kepler (1571 - 1630 ) formulated the laws of planetary motion and his work provided the foundation for Isaac Newton's theory of gravity. My point being that Kepler was a scientific giant in his days and his name will live on forever.

My current mathematical project ( personal challenge if you like ) is focused towards tilings of the plane, creating ( Mathematica ) software to print and generate tilings. And ultimately -find- new tilings I haven't seen before. There aren't many textbooks on the subject, the classic work is very recent ( in mathematical terms ), it was published in 1986: Tilings and Patterns, by Branko Grunbaum and Geoffrey C. Shephard

Earlier today I was doodling on the tiling (3,3,4,3,4) of which I uploaded a picture.
 Doodle of (3,3,4,3,4).
Then, to my surprise I read in Grunbaum / Shephard that it was Johannes Kepler (!) who started the mathematical research on tilings and patterns. One of the beautiful books Kepler wrote is called the Harmony of the World, originally published in 1619 but recently translated into English by Aiton, Duncan and Field and published the American Philosophical Society.

The Harmony of the World consists of 5 books.
- Book 1: On the construction of regular figures
- Book 2: On the congruence of regular figures
- Book 3: On the origins of the harmonic proportions, and on the nature and differences of those things which are concerned with melody
- Book 4: Preamble and explanation of the order
- Book 5: ( No title ).

This is part of a picture ( drawing ) from book 2 which has a drawing of (3, 3, 4, 3, 4 )  just like my doodle rype  marked as O ( top right ).

This proves once more that mathematics, by itself, does not change over time, its timeless. At least this part ( if not all ) of mathematics has to be discovered. The tilings of the plane have always been there, it just takes us to see them so that we can ultimately categorize them.

The fact that Kepler worked on this makes him human ( but still a giant of course ) to me, I can imagine the joy and excitement he must have felt drawing the illustrations especially since they take a lot of ( behind the scenes ) calculations.

## Welcome to The Bridge

Mathematics: is it the fabric of MEST?
This is my voyage
My continuous mission
To uncover hidden structures
To create new theorems and proofs
To boldly go where no man has gone before

(Raumpatrouille – Die phantastischen Abenteuer des Raumschiffes Orion, colloquially aka Raumpatrouille Orion was the first German science fiction television series. Its seven episodes were broadcast by ARD beginning September 17, 1966. The series has since acquired cult status in Germany. Broadcast six years before Star Trek first aired in West Germany (in 1972), it became a huge success.)