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Using Stagnation(numGenerations, true) to terminate an evolution in Watchmaker.

I would like the numGenerations to depend on how well the evolution is doing. If I have a rotten population (low fitness) then I would like to bail out early. If the population is performing well, I'd like to give it more time.

How would I do that?

I read the user manual, worked through the examples on http://watchmaker.uncommons.org/, looked at the API, and searched around the web. Didn't see this topic addressed specifically. I'm new to Java and genetic algorithms, so I could have easily missed something.

user3585533
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2 Answers2

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Rereading the API I discovered that multiple TerminationConditions can be supplied to engine.evolvePopulation(). That let me write a recursive function that keeps going as long as the fitness continues to improve.

process (Parameters params) {

    result = engine.evolvePopulation(params.size, 0, 
               new Stagnation(params.stagnation, true), 
               new TargetFitness(params.target, true));

    if (result.get(0).getFitness() >= params.target)
        process(params.increase());

    return;
}

In my case, the target is incremented by a fixed amount every time. The size and stagnation are increased as a function of the cube of the target. That way, the better a particular population becomes, the more time gets invested into it. Not sure that's the best approach, but for this problem it got the answer I was looking for.

Oh by the way, my program doesn't really look like what I pasted in above. I'm a pretty lousy programmer and my code is a lot uglier than that. Just trying to show the gist of the idea.

user3585533
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The Stagnation termination condition only aborts the evolution if the best fitness score in the population does not improve for a certain number of consecutive generations. It does not cut-off after a fixed number of generations from the start (for that you would use the GenerationCount condition), it only kicks in when the evolution appears to have stopped making progress. So if your population is performing well (by which I take it you mean that the fitness is continuing to improve) the stagnation condition is unlikely to be triggered.

If you want something different you might need to write your own TerminationCondition. It's just a single method that takes the PopulationData as an argument so that you can make decisions based on that at the end of each generation. You just need to be able to define "rotten population" in terms of the mean and/or best fitness and the number of generations so far.

Dan Dyer
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  • OK, cool. I'll try that. FYI, in my initial playing around, I set the TargetFitness to an unattainably high value, tried various population sizes and just watched it run. It always eventually stagnated, but at final fitness values of +/- 25% of the average. Given the nature of the beast, that's to be expected, right? Oh, I'm not supposed to say "thank you", but thank you anyway for making this awesome software, with its excellent documentation, available to all. – user3585533 Apr 30 '14 at 15:34