RegressionMain.java

private static final Regression<Double> REGRESSION = Regression.of(
    Regression.codecOf(OPERATIONS, TERMINALS, 5),
    Error.of(LossFunction::mse),
    Sample.ofDouble(-1.0, -8.0000),
    // ...
    Sample.ofDouble(0.9, 1.3860),
    Sample.ofDouble(1.0, 2.0000)
);

public static void main(final String[] args) {
    final Engine<ProgramGene<Double>, Double> engine = Engine
        .builder(REGRESSION)
        .minimizing()
        .alterers(
            new SingleNodeCrossover<>(0.1),
            new Mutator<>())
        .build();

    final EvolutionResult<ProgramGene<Double>, Double> result = engine
        .stream()
        .limit(Limits.byFitnessThreshold(0.01))
        .collect(EvolutionResult.toBestEvolutionResult());

    final ProgramGene<Double> program = result.getBestPhenotype()
        .getGenotype()
        .getGene();

    final TreeNode<Op<Double>> tree = program.toTreeNode();
    MathExpr.rewrite(tree); // Simplify result program.
    System.out.println("Generations: " + result.getTotalGenerations());
    System.out.println("Function:    " + new MathExpr(tree));
    System.out.println("Error:       " + REGRESSION.error(tree));
}