Symbolic regression: Mixing Bool and Double Ops

[raedma]

Hello,

I am currently facing a problem, where I would like to find a symbolic regression for a function with discontinuities, e.g.

I tried the example in HeuristicLab and it gave me a solution with basically a conditional "if x smaller than or of x greater then":

Is this possible with jenetics? At a first look I found this nice example for a setup with doubles and have seen that BoolOps are supported. However, I was unable to find an example where both operator types are mixed to later build a Regression. Regression expects a generic type, in the example Double, but I guess Boolean would work just as well with BoolOp. Is it not possible to mix Op<Double> and Op<Boolean> to build an ISeq<?> to build a Regression.codecOf(...) or would it work just with the the use of Object as the generic type?

A small hint or example would be very nice.

Regards
Martin

[jenetics]

You can try an extension to the MultiRootGP example.

static final Codec<ISeq<Function<Double[], Double>>, ProgramGene<Double>> CODEC =
    Codec.of(
        Genotype.of(
            // Discriminator
            ProgramChromosome.of(
                0,
                ISeq.of(Op.of("identity", UnaryOperator.identity())),
                ISeq.of(EphemeralConst.of(() -> (double)RandomRegistry.random().nextInt(100)))
            ),
            // First 'program'
            ProgramChromosome.of(
                5,
                ch -> ch.root().size() <= 50,
                OPERATIONS,
                TERMINALS
            ),
            // Second 'program'
            ProgramChromosome.of(
                5,
                ch -> ch.root().size() <= 50,
                OPERATIONS,
                TERMINALS
            )
        ),
        gt -> gt.stream()
            .map(Chromosome::gene)
            .collect(ISeq.toISeq())
    );

static double fitness(final ISeq<Function<Double[], Double>> programs) {
    final var discriminator = programs.get(0).apply(new Double[] {0.0});
    if (discriminator <= 50) {
        // Evaluate programs.get(1)
        return 1;
    } else {
        // Evaluate program.get(2)
        return 2;
    }
}