# The Code part 3

This week’s review of The Code has been delayed a day as I was at the cinema on Wednesday night. Saw Super 8, the new film from JJ Abrams. Like others films he has directed it’s a good film. I always hope that one day he might do a great film – this isn’t it.

Back to the TV review. In this week’s programme we saw Marcus du Sautoy risk his life to show his belief in “The Code” when he calculated where a 30kg ball would land and sat just beyond the landing spot. Given that the series has used special graphics effects (this week was full of “tilt shift” effects where the focus has been monkeyed around with to achieve a miniaturization look) one may doubt the event. Particularly as later in the programme effects were used on the ball to make it fall short and go into orbit. However, it did look like he really did the stunt! Quite brave for a man who says he can’t do arithmetic.

Anyhow, leaving aside the distractions, what was the show about? Prediction mainly. When can we use mathematics to predict what will happen? Quite often is of course the answer. Du Sautoy brought in Christopher Columbus, starling flocks, ants, rock-paper-scissors, serial killers, chaos, lemmings, weather prediction, the butterfly effect, the wisdom of crowds, forecasting flu with Google (the number of web searches for flu symptoms and remedies follows the incidence of flu in the population – fancy that!) and looking for patterns in cities. The latter featured an interview with Geoffrey West who recently gave a TED talk. (I think the talk will feature in my new course on making presentations as an example of what not to do!)

Most of the uses of mathematics were legitimate but the use in catching criminals seemed dubious. The example given involved using the seemingly random locations of the 36 Mardi Gra [sic] bombs in the 90s to predict the location of the bomber or bombers. It turned out that the bombers lived close to the area predicted by the mathematics. Unfortunately, the predicted area was huge and would have been of no use to police, and in fact the bombers were caught in the end by good old-fashioned coppering. It was the sort of result that looked good in hindsight, more of a postdiction than a prediction!

More successful was the prediction of the volatility of lemming populations. It has been known for many years that Disney faked the famous lemming suicide film and so the suicide explanation for huge variation of the lemming population is of no use.

In case you weren’t taking notes, the population is modelled by the logistic equation (or map) which is

$P_{{\text{next}}}=RP(1-P)$

where $P$ is the total population, $P_{{\text{next}}}$ is the population in the next cycle, and $R$ is the population growth rate. The value $R=2$ gives a nice and steady population, $R=3.1$ gives an oscillation and $R=3.57$ gives chaos, which is what we see for the lemmings.

So that’s it, the series is over. All that is left is for someone to use the clues, break the code and find the hidden treasure. Hmmm, was that a 6 in the bird flock?