Henri Poincaré described a beautiful geometric model with some intriguing properties. He envisioned a circular disk in the Euclidean plane, where distances were distorted to give it geometric properties quite different from those of Euclid’s *Elements*. He supposed that the temperature varied linearly from a fixed value at the centre of the disk to absolute zero on the boundary, and that lengths varied in proportion to the temperature.

## Archive for April, 2022

### The Whole is Greater than the Part — Or is it?

Published April 21, 2022 Irish Times ClosedTags: Cantor, Geometry, Set Theory

Euclid flourished about fifty years after Aristotle and was certainly familiar with Aristotle’s Logic. Euclid’s organization of the work of earlier geometers was truly innovative. His results depended upon basic assumptions, called axioms and “common notions”. There are in total 23 definitions, five axioms and five common notions in *The Elements*. The axioms, or postulates, are specific assumptions that may be considered as self-evident, for example “the whole is greater than the part” [TM232 or search for “thatsmaths” at irishtimes.com]. Continue reading ‘The Whole is Greater than the Part — Or is it?’

### Following the Money around the Eurozone

Published April 14, 2022 Occasional ClosedTags: modelling, Numerical Analysis

Take a fistful of euro coins and examine the obverse sides; you may be surprised at the wide variety of designs. The eurozone is a monetary union of 19 member states of the European Union that have adopted the euro as their primary currency. In addition to these countries, Andorra, Monaco, San Marino and Vatican City use euro coins so, from 2015, there have been 23 countries, each with its own national coin designs. For the €1 and €2 coins, there are 23 distinct national patterns; for the smaller denominations, there are many more. Thus, there is a wide variety of designs in circulation.

### Mamikon’s Visual Calculus and Hamilton’s Hodograph

Published April 7, 2022 Occasional ClosedTags: Analysis, Mechanics

[This is a condensed version of an article [5] in *Mathematics Today*]

A remarkable theorem, discovered in 1959 by Armenian astronomer Mamikon Mnatsakanian, allows problems in integral calculus to be solved by simple geometric reasoning, without calculus or trigonometry. Mamikon’s Theorem states that *`The area of a tangent sweep of a curve is equal to the area of its tangent cluster’.* We shall illustrate how this theorem can help to solve a range of integration problems.

Continue reading ‘Mamikon’s Visual Calculus and Hamilton’s Hodograph’