Method select

tools/yulPhaser/GeneticAlgorithms.cpp:141–175

}

Population ClassicGeneticAlgorithm::select(Population _population, size_t _selectionSize)
{
	if (_population.individuals().size() == 0)
		return _population;

	size_t maxFitness = 0;
	for (auto const& individual: _population.individuals())
		maxFitness = std::max(maxFitness, individual.fitness);

	size_t rouletteRange = 0;
	for (auto const& individual: _population.individuals())
		// Add 1 to make sure that every chromosome has non-zero probability of being chosen
		rouletteRange += maxFitness + 1 - individual.fitness;

	std::vector<Individual> selectedIndividuals;
	for (size_t i = 0; i < _selectionSize; ++i)
	{
		size_t ball = SimulationRNG::uniformInt(0, rouletteRange - 1);

		size_t cumulativeFitness = 0;
		for (auto const& individual: _population.individuals())
		{
			size_t pocketSize = maxFitness + 1 - individual.fitness;
			if (ball < cumulativeFitness + pocketSize)
			{
				selectedIndividuals.push_back(individual);
				break;
			}
			cumulativeFitness += pocketSize;
		}
	}

	assert(selectedIndividuals.size() == _selectionSize);
	return Population(_population.fitnessMetric(), selectedIndividuals);
}