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Hi Adrián,

The problem is that NSGA2 expects to be working with Fitness objects that are specifically of type NSGA2Fitness (which is itself a subclass of MultiObjectiveFitness).

If you have your CustomFitness class inherent from NSGA2Fitness instead of MultiObjectiveFitness, you should be good to go.

Thanks,
Siggy

On Sun, Dec 9, 2018 at 4:38 PM Adrián Romero Cáceres <[log in to unmask]> wrote:
Hello!

I have implemented a new betterThan operator into a CustomFitness class,
which is an extended class of MultiObjectiveFitness.  I wrote 
pop.subpop.0.species.fitness = ec.multiobjective.CustomFitness inside my
experiment param file. Once the execution starts, after the first
generation fails, returning the next error:

Exception in thread "main" java.lang.ClassCastException:
ec.multiobjective.CustomFitness cannot be cast to
ec.multiobjective.nsga2.NSGA2MultiObjectiveFitness
         at
ec.multiobjective.nsga2.NSGA2Breeder.assignFrontRanks(NSGA2Breeder.java:185)
         at
ec.multiobjective.nsga2.NSGA2Breeder.buildArchive(NSGA2Breeder.java:121)
         at
ec.multiobjective.nsga2.NSGA2Breeder.loadElites(NSGA2Breeder.java:82)
         at ec.simple.SimpleBreeder.breedPopulation(SimpleBreeder.java:225)
         at
ec.multiobjective.nsga2.NSGA2Breeder.breedPopulation(NSGA2Breeder.java:113)
         at
ec.simple.SimpleEvolutionState.evolve(SimpleEvolutionState.java:104)
         at ec.EvolutionState.run(EvolutionState.java:482)
         at ec.Evolve.main(Evolve.java:771)

I forgot something? Is it the right way to extend the betterThan operator?

Thanks in advance,
Adrián.


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Doctoral Candidate, George Mason University