Elitism in GA: Should I let the elites be selected as parents?
I am a little confused by the elitism concept in Genetic Algorithm (and other evolutionary algorithms). When I reserve and then copy 1 (or more) elite individuals to the next generation,
- Should I consider the elite solution(s) in the parent selection of the current generation (making a new population)?
- Or, should I use others (putting the elites aside) for making a new population and just copy the elites directly to the next generation?
If the latter, what is the use of elitism? Is it just for not losing the best solution? Because in this scheme, it won't help the convergence at all.
for example, here under the crossover/mutation part, it is stated that the elites aren't participating.
(Of course, the same question can be asked about the survivor selection part.)
Answer
Elitism only means that the most fit handful of individuals are guaranteed a place in the next generation - generally without undergoing mutation. They should still be able to be selected as parents, in addition to being brought forward themselves.
That article does take a slightly odd approach to elitism. It suggests duplicating the most fit individual - that individual gets two reserved slots in the next generation. One of these slots is mutated, the other is not. That means that, in the next generation, at least one of those slots will reenter the general population as a parent, and possibly two if both are overtaken.
It does seem a viable approach. Either way - whether by selecting elites as parents while also perpetuating them, or by copying the elites and then mutating one - the elites should still be closely attached to the population at large so that they can share their beneficial genes around.
@Peladao's answer and comment are also absolutely spot on - especially on the need to maintain diversity and avoid premature convergence, and the elites should only represent a small portion of the population.