How to distribute the fitness evaluation using Mahout.GA

In any Watchmaker program, you'll have to create an instance of a StandaloneEvolutionEngine. For the TSP example this is done in the EvolutionaryTravellingSalesman class:

private EvolutionEngine<List<String>> getEngine(CandidateFactory<List<String>> candidateFactory, EvolutionaryOperator<List<?>> pipeline, Random rng) {
  return new StandaloneEvolutionEngine<List<String>>(candidateFactory, pipeline, new RouteEvaluator(distances), selectionStrategy, rng);
}

The RouteEvaluator class is where the fitness of each individual is evaluated, if we want to distribute the evaluation over a Hadoop Cluster, all we have to is wrap the evaluator in a MahoutFitnessEvaluator, and instead of a StandaloneEvolutionEngine we'll use a STEvolutionEngine :

private EvolutionEngine<List<String>> getEngine(CandidateFactory<List<String>> candidateFactory, EvolutionaryOperator<List<?>> pipeline, Random rng) {
  MahoutFitnessEvaluator<List<String>> evaluator = new MahoutFitnessEvaluator<List<String>>(new RouteEvaluator(distances));
  return new STEvolutionEngine<List<String>>(candidateFactory, pipeline, evaluator, selectionStrategy, rng);
}

And voila! your code is ready to run on Hadoop. The complete running example is available with the examples in the org/apache/mahout/ga/watchmaker/travellingsalesman directory