(email to my fellow researchers)
Subject: premature convergence
No, this email is not about some “teenage” problem :)
Per my conversation with Emmanuel today, the classic Kepler’s 3rd Law of Planetary Motion (called the “Harmonies Law”) is the square of the period divided by the cube of the mean radius from the center of the Sun to the center of the planet.
My new “minimisation’ function is working beautifully! However, maybe it works a little too well. Karoo GP is quickly converging on p/p (period divided by period) which of course equals 1, where 6 of the 9 planets are defined as 1.0 in the dataset I am using (the other 3 planets are 0.99 or 0.98).
So, I am going to introduce a new user defined “Min Nodes” which will set the minimum number of nodes (elements) in the GP tree (equation). I feel like this is cheating, but Emmanuel confirmed that most GP problems require some tweaking of the code.
There are 2 ways a large tree can very quickly get smaller: Grow Mutation or Cross-Over mutation (Reproduction, Point Mutation, and Full Mutation do not alter Tree size). I can intercept either of these and force them to evolve again and again until the new tree is above the min boundary; or simply invoke an artificial fitness boost in the right direction.
What would Darwin say? What would Gandhi do?
It seems to invoke evolutionary pressure is the one more like the “real-world”, no? To force something to evolve again and again until it satisfies a certain criteria is a bit convoluted. But any more so than defining a maximum depth?
We’ll see how I feel in the morning :)
(continued in Premature convergence)