I have just learned from the Mathematics Genealogy Project that I am one of 92526 descendants of Friedrich Leibniz.

**Alexandre Borovik**| February 21, 2012

## Mathematics Genealogy

Posted in Uncategorized

**Alexandre Borovik**| February 16, 2012

## Ian Stewart: The mathematical equation that caused the banks to crash

Ian Stewart in the The Observer Sunday February 12 2012:

The Black-Scholes equation was the mathematical justification for the trading that plunged the world’s banks into catastrophe

It was the holy grail of investors. The Black-Scholes equation, brainchild of economists Fischer Black and Myron Scholes, provided a rational way to price a financial contract when it still had time to run. It was like buying or selling a bet on a horse, halfway through the race. It opened up a new world of ever more complex investments, blossoming into a gigantic global industry. But when the sub-prime mortgage market turned sour, the darling of the financial markets became the Black Hole equation, sucking money out of the universe in an unending stream.

Read more in The Guardian.

[with thanks to muriel]

Posted in Uncategorized

**Alexandre Borovik**| February 16, 2012

## Aaron Sloman on vision.

A recent talk by Aaron Sloman,

What is vision for, and how does it work? Some considerations for philosophy of perception [600 kB PDF].

With thanks to Seb Schmoller.

Posted in Uncategorized

**Alexandre Borovik**| February 11, 2012

## Cinderella and GeoGebra

[*My ancient post (December 17, 2006) from a now defunct blog on Blogger:* ]

In his comment on one of my previous posts, *Euclid’s Elements, Interactive*, Rick Booth brought my attention to *GeoGebra*, a free interactive geometry package. *GeoGebra* is nice, simple, intuitive to use, and could be a great help at school.

For some years, I was an occasional user of a commercial package, *Cinderella*. I decided to run a quick comparision of the two packages on a problem about the radical axis of two circles — I briefly mention the problem in my book. The problem is easy to solve with some help from Pythagoras:

Prove that the set of points

Pin the plane such that the tangents fromPto two given non-intersecting circles are equal, is a straight line (it is called the radical axis of the two circles).

The problem is even easier when the two circles intersect – in that case, the radical axis is exactly the line through the two points of intersection. And in the case of tangent circles it is even easier — in that case the radical axis is the common tangent line.

It is interesting to compare the behaviour, in *Cinderella* and *GeoGebra*, of a simple interactive diagram: two interesecting circles of varying radii and the straight line determined by their points of intersection. In *GeoGebra*, when you vary the radii or move the centers of the circles and make the circles non-intersecting, the line through the points of intersection disappears — exactly as one should expect. In *Cinderella*, the line does not disappear, it moves following the movements of the circles, always separating them; when circles touch each other and start to intersect again, the line happens to be, again, the tangent line or the line through the points of intersection. And it is exactly the radical axis of the two circles!

I have not read documentation for *GeoGebra*, but the behaviour of this diagram suggests that, in *GeoGebra* (at least in the default mode), the underlying mathematical structure is the honest real Euclidean plane. In *Cinderella*, the underlying structure is the complex projective plane; what we see on the screen is just its tiny fragment, a real affine part. The radical axis of two non-intersecting circles is the real part of the complex line through two complex points of intersection; since the intersection points of two real circles are complex conjugate, the line is invariant under complex conjugation and therefore is real and shows up on the real Euclidean plane.

The Help Index of *GeoGebra* says about complex numbers:

GeoGebra does not support complex numbers directly, but you may use points to simulate operations with complex numbers.

However, even if one cannot do in *GeoGebra* the complex tricks of *Cinderella*, it is not a serious drawback — one should work hard to find a problem, of a secondary school level, where the difference in the nature of real and complex mathematical engines becomes visible. Such a problemis likely to involve circles or other conics, that is, quadratic equations — but remember, even the distance function is already involving a quadratic form, therefore complex numbers can pop up in rather unexpected places.

[I can add that another problem:

find the points of kiss of three mutually tangential cirles with centers at three given points

is linear, not quadratic, and can be solved by affine tools, say, with the help of a ruler with two parallel edges. ]

But still, when assessing software for mathematics teaching, it is useful to check the power, both computational and theoretical, of the mathematical engine. Unfortunately, most reviews of software for mathematics teaching never discuss this point.

To finish on a note more suitable for the festive season, I wish to mention that, in my book, radical axes appear in a solution of the following problem:

The Holes in the Cheese Problem.A big cubic piece of cheese has some spherical holes inside (like Swiss Emmental cheese, say). Prove that you can cut it into convex polytopes in such way that every polytope contains exactly one hole.

The previous discussion is the strongest hint for its solution.

And finally, a quote from Cheese.com:

“Emmental […] is considered to be one of the most difficult cheeses to be produced because of its complicated hole-forming fermentation process.”

Is it realy surprising that compex numbers naturally appear in the cutting the wheel of cheese?

Posted in Uncategorized | Tags: Cinderella, Complex conjugate, Euclid, GeoGebra, Geometry, Mathematics, Tangent

**Alexandre Borovik**| February 3, 2012

## Antikythera Mechanism: A talk in Manchester

In April, the British Colloquium for Theoretical Computer Science will be held in Manchester. The webpage. Fees are quite reasonable (they essentially just cover the conference banquet, lunches and drinks provided).

We have a speaker, Mike Edmunds , involved with the fascinating investigation of the Antikythera Mechanism. Below is the abstract of his talk, The Antikythera Mechanism and the early history of mechanical computing:

Perhaps the most extraordinary surviving relic from the ancient Greek world is a device containing over thirty gear wheels dating from the late 2nd century B.C., and now known as the Antikythera Mechanism. This device is an order of magnitude more complicated than any surviving mechanism from the following millennium, and there is no known precursor. It is clear from its structure and inscriptions that its purpose was astronomical, including eclipse prediction. In this illustrated talk, I will outline the results – including an assessment of the accuracy of the device – from our international research team, which has been using the most modern imaging methods to probe the device and its inscriptions. Our results show the extraordinary sophistication of the Mechanism’s design. There are fundamental implications for the development of Greek astronomy, philosophy and technology. The subsequent history of mechanical computation will be briefly sketched, emphasising both triumphs and lost

opportunities……

Posted in Uncategorized | Tags: Antikythera Mechanism, Archaeology, Manchester

**Alexandre Borovik**| January 21, 2012

## Exams and league tables

Nick Gibb MP, State Minister for Schools, published an article in the The Telegraph, outlining a reform of school league tables.

an article is followed by an interesting comment from JD:

If it is possible to “teach to a test” at the expense of a subject, then the fault is with the test.

They must simply be testing facts rather than any understanding.

I’ve discussed this with my engineers who inform me they had very different finals for their Masters than I did.

The norm is multi choice and exams with 30 questions expecting fact recital.

From 30 years ago the emphasis was on very short questions expecting an essay for an answer. Classically this question would be to discuss methods to solve a problem that as yet hasn’t been solved (in this case using the engineering skills you’ve learnt).

I remember 30 years ago being asked one question with a 1 1/2 hour essay.

“Your director of engineering proposes a new product. A Digital Network Telephone with IP Packet based data. Discuss.”

This was years before TBL proposed the WWW – we were being asked to invent Skype in 1.5 hours. This type of question isn’t possible to teach to – especially as the list of problems to be solved is endless.

In the same vein, I had to appraise a Navigation specialist whilst working offshore. He happened to be Malay (this was in Asia). He had a Masters Science degree. We asked him to solve a simple problem with the tools available offshore.

“The ships gyro has failed. How would you use the vessels onboard GPS systems and additional GPS to functionally replace the Gyro providing heading information”.

He couldn’t provide any answer (after two weeks). His excuse was there was no reference to this in any book. He said then the question wasn’t fair – how can you answer a question where you can’t find the answer in a book?

This is where education has gone wrong.

Posted in Uncategorized | Tags: Global Positioning System, GPS, Multiple choice, Question, Skype

**Alexandre Borovik**| January 16, 2012

## Bertrand Russell on BBC

**Alexandre Borovik**| January 11, 2012

## Mathematical Pasta

The NYT, *Pasta Graduates From Alphabet Soup to Advanced Geometry* by KENNETH CHANG.

You got the idea. George L. Legendre’s book: Pasta by Design.

[With thanks to to muriel]

Posted in Uncategorized

**Alexandre Borovik**| January 11, 2012

## Manual dexterity, II

This is a continuation of the previous post.

Among horrors proudly shown at the recent Computer Based Math Education Summit was a software package for primary school where pupils were supposed to enter numeric answers by moving, with a computer mouse, beads on a virtual number rack (two-string abacus) on the computer screen. Maria Montessori introduced number rack for enhancing pupils’ **TACTILE** perception of number!

Posted in Uncategorized | Tags: Education, Maria Montessori, Montessori method

**Alexandre Borovik**| January 11, 2012

## Manual dexterity

From an interview with Professor Heinz Wolff in the Engineering & Technology, an in-house magazine of IET.

After the brain, Wolff explains, the ‘most marvellous thing we have’ is the hand: an actuator that can thread a needle one minute or wield a sledgehammer the next without modification. ‘I firmly believe that the continual iteration of hand-eye-brain is how we became

Homo sapiens.‘We started to make tools, acquired manual skills and could imagine a tool that would be better. And then there was a very important point in our development, which was that we could imagine a tool that could make a tool, which could then make something. This is a very sophisticated way of thinking.’ His obvious implication is that this is the origin of engineering.

His hands flash across a QWERTY keyboard. ‘Apart from typing, we don’t use our hands. Girls don’t embroider; boys don’t play with Meccano. With these things you effectively develop an eye at the end of the finger, and you do this when you’re seven years old. And it’s really very clever. But it’s gone.’

Wolff has lectured on the ‘death of competence’ and he thinks it’s brought about by the abandonment of micromanipulation – doing something small and critical with the hand. ‘Our engineering students can’t make things. They might be able to design things on a computer, but they can’t make things. And I don’t believe that you can be an engineer properly, in terms of it circulating in your blood and your brain, without having a degree of skill in making things.’ He explains that this is why apprenticeships were so good, because ‘you actually made things while learning a bit of the theory’.

In neglecting to teach basic manual skills we are producing a generation that carries the seeds of its own impotence. Wolff believes that whilst all teachers agree children should be articulate and use language with precision and skill, ‘they don’t attach the same values to the use of their hands.’

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