blt-gp/examples/gp_symbolic_regression_example.cpp

/*
 *  <Short Description>
 *  Copyright (C) 2024  Brett Terpstra
 *
 *  This program is free software: you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation, either version 3 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program.  If not, see <https://www.gnu.org/licenses/>.
 */
#include <blt/gp/program.h>
#include <blt/gp/tree.h>
#include <blt/std/logging.h>
#include <iostream>

static constexpr long SEED = 41912;

struct context
{
    float x, y;
};

std::array<context, 200> fitness_cases;

blt::gp::prog_config_t config = blt::gp::prog_config_t()
        .set_initial_min_tree_size(2)
        .set_initial_max_tree_size(6)
        .set_elite_count(0)
        .set_max_generations(50)
        .set_pop_size(500);

blt::gp::type_provider type_system;
blt::gp::gp_program program(type_system, blt::gp::random_t{SEED}, config); // NOLINT

blt::gp::operation_t add([](float a, float b) { return a + b; }, "add");
blt::gp::operation_t sub([](float a, float b) { return a - b; }, "sub");
blt::gp::operation_t mul([](float a, float b) { return a * b; }, "mul");
blt::gp::operation_t pro_div([](float a, float b) { return b == 0.0f ? 1.0f : a / b; }, "div");
blt::gp::operation_t op_sin([](float a) { return std::sin(a); }, "sin");
blt::gp::operation_t op_cos([](float a) { return std::cos(a); }, "cos");
blt::gp::operation_t op_exp([](float a) { return std::exp(a); }, "exp");
blt::gp::operation_t op_log([](float a) { return a == 0.0f ? 0.0f : std::log(a); }, "log");

blt::gp::operation_t lit([]() {
    return program.get_random().get_float(-320.0f, 320.0f);
}, "lit");
blt::gp::operation_t op_x([](const context& context) {
    return context.x;
}, "x");

constexpr auto fitness_function = [](blt::gp::tree_t& current_tree, blt::gp::fitness_t& fitness, blt::size_t index) {
    constexpr double value_cutoff = 1.e15;
    for (auto& fitness_case : fitness_cases)
    {
        auto diff = std::abs(fitness_case.y - current_tree.get_evaluation_value<float>(&fitness_case));
        if (diff < value_cutoff)
        {
            fitness.raw_fitness += diff;
            if (diff < 0.01)
                fitness.hits++;
        } else
            fitness.raw_fitness += value_cutoff;
    }
    fitness.standardized_fitness = fitness.raw_fitness;
    fitness.adjusted_fitness = 1.0 / (1.0 + fitness.standardized_fitness);
    //BLT_TRACE("fitness: %lf raw: %lf", fitness.adjusted_fitness, fitness.raw_fitness);
};

float example_function(float x)
{
    return x * x * x * x + x * x * x + x * x + x;
}

int main()
{
    for (auto& fitness_case : fitness_cases)
    {
        constexpr float range = 10;
        constexpr float half_range = range / 2.0;
        auto x = program.get_random().get_float(-half_range, half_range);
        auto y = example_function(x);
        fitness_case = {x, y};
    }
    
    type_system.register_type<float>();
    
    blt::gp::operator_builder<context> builder{type_system};
    builder.add_operator(add);
    builder.add_operator(sub);
    builder.add_operator(mul);
    builder.add_operator(pro_div);
    builder.add_operator(op_sin);
    builder.add_operator(op_cos);
    builder.add_operator(op_exp);
    builder.add_operator(op_log);
    
    builder.add_operator(lit, true);
    builder.add_operator(op_x);
    
    program.set_operations(builder.build());
    
    program.generate_population(type_system.get_type<float>().id(), fitness_function);
    
    while (!program.should_terminate())
    {
        program.create_next_generation(blt::gp::select_fitness_proportionate_t{}, blt::gp::select_fitness_proportionate_t{}, blt::gp::select_fitness_proportionate_t{});
        program.next_generation();
        program.evaluate_fitness();
    }
    
    auto best = program.get_best_individuals<3>();
    
    BLT_INFO("Best approximations:");
    for (auto& i_ref : best)
    {
        auto& i = i_ref.get();
        BLT_DEBUG("Fitness: %lf, stand: %lf, raw: %lf", i.fitness.adjusted_fitness, i.fitness.standardized_fitness, i.fitness.raw_fitness);
        i.tree.print(program, std::cout);
        std::cout << "\n";
    }
    
    return 0;
}