## Archive for June, 2022

### Can We Control the Weather?

Atmospheric motions are chaotic: a minute perturbation can lead to major changes in the subsequent evolution of the flow. How do we know this? There is just one atmosphere and, if we perturb it, we can never know how it might have evolved if left alone.

We know, from simple nonlinear models that exhibit chaos, that the flow is very sensitive to the starting conditions. We can run “identical twin” experiments, where the initial conditions for two runs are almost identical, and watch how the two solutions diverge. This — and an abundance of other evidence — leads us to the conclusion that the atmosphere behaves in a similar way.

### The Arithmetic Triangle is Analytical too

Pascal’s triangle is one of the most famous of all mathematical diagrams. It is simple to construct and rich in mathematical patterns. There is always a chance of finding something never seen before, and the discovery of new patterns is very satisfying.

Not too long ago, Harlan Brothers found Euler’s number ${e}$ in the triangle (Brothers, 2012(a),(b)). This is indeed surprising. The number ${e}$ is ubiquitous in analysis but it is far from obvious why it should turn up in the arithmetic triangle.

### ICM 2022 — Plans Disrupted but not Derailed

In just three weeks the largest global mathematical get-together will be under way. The opening ceremony of the 2022 International Congress of Mathematicians (ICM) opens on Wednesday 6 July and continues for nine days. Prior to the ICM, the International Mathematical Union (IMU) will host its 19th General Assembly in Helsinki on 3–4 July [TM234 or search for “thatsmaths” at irishtimes.com].

### Swingin’-Springin’-Twistin’-Motion

{Left: Swinging spring (three d.o.f.). Right: the Wilberforce spring (two d.o.f.).

The swinging spring, or elastic pendulum, exhibits some fascinating dynamics. The bob is free to swing like a spherical pendulum, but also to bounce up and down due to the stretching action of the spring. The behaviour of the swinging spring has been described in a previous post on this blog [Reference 1 below].

### Parity of the Real Numbers: Part I

In some recent posts, here and here we discussed the extension of the concept of parity (Odd v. Even) from the integers to the rational numbers. We found that it is natural to consider three parity classes, determined by the parities of the numerator and denominator of a rational number ${q = m / n}$ (in reduced form):

• q Odd: ${m}$ odd and ${n}$ odd.
• q Even: ${m}$ even and ${n}$ odd.
• q None: ${m}$ odd and ${n}$ even.

or, in symbolic form,

$\displaystyle \mbox{Odd} = \frac{odd}{odd} \,, \qquad \mbox{Even} = \frac{even}{odd} \,, \qquad \mbox{None} = \frac{odd}{even}$

Here, ${None}$ stands for “Neither Odd Nor Even”.