RealFunction.java

import static java.lang.Math.PI;
import static java.lang.Math.cos;
import static java.lang.Math.sin;
import static org.jenetics.engine.EvolutionResult.toBestPhenotype;
import static org.jenetics.engine.limit.bySteadyFitness;

import org.jenetics.DoubleGene;
import org.jenetics.MeanAlterer;
import org.jenetics.Mutator;
import org.jenetics.Optimize;
import org.jenetics.Phenotype;
import org.jenetics.engine.Engine;
import org.jenetics.engine.EvolutionStatistics;
import org.jenetics.engine.codecs;
import org.jenetics.util.DoubleRange;

public class RealFunction {

	// The fitness function.
	private static double fitness(final double x) {
		return cos(0.5 + sin(x))*cos(x);
	}

	public static void main(final String[] args) {
		final Engine<DoubleGene, Double> engine = Engine
			// Create a new builder with the given fitness
			// function and chromosome.
			.builder(
				RealFunction::fitness,
				codecs.ofScalar(DoubleRange.of(0.0, 2.0*PI)))
			.populationSize(500)
			.optimize(Optimize.MINIMUM)
			.alterers(
				new Mutator<>(0.03),
				new MeanAlterer<>(0.6))
			// Build an evolution engine with the
			// defined parameters.
			.build();

		// Create evolution statistics consumer.
		final EvolutionStatistics<Double, ?>
			statistics = EvolutionStatistics.ofNumber();

		final Phenotype<DoubleGene, Double> best = engine.stream()
			// Truncate the evolution stream after 7 "steady"
			// generations.
			.limit(bySteadyFitness(7))
			// The evolution will stop after maximal 100
			// generations.
			.limit(100)
			// Update the evaluation statistics after
			// each generation
			.peek(statistics)
			// Collect (reduce) the evolution stream to
			// its best phenotype.
			.collect(toBestPhenotype());

		System.out.println(statistics);
		System.out.println(best);
	}
}