how to find two optimal parameters with jenetics ?

[ZUOJIANYI]

No description provided.

[ZUOJIANYI]

here the code, can anyone help me? thanks
`
public double fitness(double C, double gamma) {

    problem = scaler.scale(runoff, rain, evap, rbye, rde, doub_rain, doub_evap, doub_rainbye, doub_evapbyr, triple_rain, triple_evap);
    param.svm_type = SvmParameter.EPSILON_SVR;
    param.kernel_type = SvmParameter.RBF;
    param.cache_size = 500;
    param.eps = 0.01;
    param.C = Math.pow(2,C);
    param.gamma = Math.pow(2,gamma);


    CrossValidation cv = new CrossValidation();
    cv.doCrossValidation(problem,param,5);

    return cv.getCVSCC();
}

public void testGA(){

    final Engine<DoubleGene,Double> engine = Engine
            .builder(GetMonthDataForQPE::fitness,
                    codecs.ofScalar(DoubleRange.of(-8.0,8.0)),codecs.ofScalar(DoubleRange.of(-8.0,8.0)))
            .populationSize(500)
            .optimize(Optimize.MAXIMUM)
            .alterers(
                    new Mutator<>(0.03),
                    new MeanAlterer(0.6)
            )
            .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);

}

`

[ZUOJIANYI]

In the mthond 'testGA', i got the error with Engine.builder:
Cannot resolve method 'builder(, org.jenetics.engine.Codec<java.lang.Double,org.jenetics.DoubleGene>, org.jenetics.engine.Codec<java.lang.Double,org.jenetics.DoubleGene>)'

[jenetics]

The main problem with your code was, that the fitness function can only take one parameter. If you want to have more, you have to wrap it into an array:

static double fitness(final double[] params) {
    final double C = params[0];
    final double gamma = params[1];

    // Your fitness calculation.
    return C + gamma;
}

The fixed program would look like this:

public class GetMonthDataForQPE {

    static double fitness(final double[] params) {
        final double C = params[0];
        final double gamma = params[1];
    
        // Your fitness calculation.
        return C + gamma;
    }

    public static void main(final String[] args) {
        codecs.ofVector(DoubleRange.of(-8.0, 8.0), 2);

        final Engine<DoubleGene, Double> engine = Engine
            .builder(
                GetMonthDataForQPE::fitness,
                codecs.ofVector(DoubleRange.of(-8.0, 8.0), 2))
            .populationSize(500)
            .optimize(Optimize.MAXIMUM)
            .alterers(
                    new Mutator<>(0.03),
                    new MeanAlterer<>(0.6)
                )
            .build();


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

        final Phenotype<DoubleGene, Double> best = engine.stream()
            .limit(bySteadyFitness(7))
            .limit(100)
            .peek(statistics)
            .collect(toBestPhenotype());

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

}