Monday 31 August 2020

Mutant algorithms

 The word "algorithm" has caused a storm in recent news in the UK. Due to COVID-19 school children were not able to sit their exams. This left 16 and 18 year olds waiting to see how they would be assessed, and had obvious implications for their academic or career futures.  As you may know, the grades were awarded based on an "algorithm", which our Prime Minister later described as mutant. According to the BBC news, he said "'Mutant algorithm' caused exam chaos." This begs the question, what does our PM think a mutant algorithm is?

The news in the UK has talked generally about the algorithm's inputs being course work and teacher's estimated grades. These are "mutated" (or adjusted) by the algorithm to take into account a school's performance over the last three years. This means schools whose pupils sometimes struggle are more likely to be down-graded. The precise details are buried in a 319 page report. Feel free to read it all and report back. TL;DR; Private and public schools tend to get higher grades than government run schools, so poorer pupils tended to get down-graded and richer pupils did not. Some form of mutation, or even perversion, perhaps of justice, but not in the algorithm. 

Now, some algorithms do use mutation. In fact genetic algorithms rely on mutation to seek out new solutions to problems. This is guided by a fitness function, to check the "mutant algorithm" is doing what's required. You can test such algorithms to see what they do, and keep an eye on them as they run to check they are heading the right way. You frequently spend a long time tuning parameters to get better results. This, on the face of it, has nothing whatsoever to do with the "mutant algorithm" our PM was talking about. 

There has also be a hint of slur on the programmers who wrote the algorithm, suggesting the idea was good and proper but the naughty programmers took it upon themselves to do something completely different that got out of hand, like a Marvel movie. Think Magneto (naughty programmers) versus Charles Francis Xavier (sensible people like, our PM? Go figure). I am sick of programmer bashing and the general misunderstanding of algorithms.

Where a genetic algorithm uses mutation, or a Monte Carlo simulation uses random numbers as input, it is still possible to test the algorithm is doing what you require. Programmers should never abdicate responsibility for what they have built. However, it is highly irresponsible of the news to allow propaganda and misrepresentations to flourish like this. 

A while ago, the Imperial College model for COVID-19 was open-sourced. At the time many people raised bug reports against it. One rumour suggested that running it twice with the same seed for the pseudo-random numbers would produce different results. Now, that might be described as a "mutant algorithm", but we'd usually describe this as buggy code. I don't believe our PM has the technical know-how to spot buggy code, but I'm willing to help him out if he wants. I'm also willing to be interviewed by the BBC to explain some of these technical issues in more detail, if they are interested. Or I could find other technical people who could equally well help out.

DM me.


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