std::vector<population::individual_type> hv_greedy_s_policy::select(population &pop) const
{
// Fall back to best_s_policy when facing a single-objective problem.
if (pop.problem().get_f_dimension() == 1) {
return best_s_policy(m_rate, m_type).select(pop);
}
pagmo_assert(get_n_individuals(pop) <= pop.size());
// Gets the number of individuals to select
const population::size_type migration_rate = get_n_individuals(pop);
// Create a temporary array of individuals.
std::vector<population::individual_type> result;
// Indices of fronts.
std::vector< std::vector< population::size_type> > fronts_i = pop.compute_pareto_fronts();
// Fitness vectors of individuals according to the indices above.
std::vector< std::vector< fitness_vector> > fronts_f (fronts_i.size());
// Nadir point is established manually later, first point is as a first "safe" candidate.
fitness_vector refpoint(pop.get_individual(0).cur_f);
for (unsigned int f_idx = 0 ; f_idx < fronts_i.size() ; ++f_idx) {
fronts_f[f_idx].resize(fronts_i[f_idx].size());
for (unsigned int p_idx = 0 ; p_idx < fronts_i[f_idx].size() ; ++p_idx) {
fronts_f[f_idx][p_idx] = fitness_vector(pop.get_individual(fronts_i[f_idx][p_idx]).cur_f);
// Update the nadir point manually for efficiency.
for (unsigned int d_idx = 0 ; d_idx < fronts_f[f_idx][p_idx].size() ; ++d_idx) {
refpoint[d_idx] = std::max(refpoint[d_idx], fronts_f[f_idx][p_idx][d_idx]);
}
}
}
// Epsilon is added to nadir point
for (unsigned int d_idx = 0 ; d_idx < refpoint.size() ; ++d_idx) {
refpoint[d_idx] += m_nadir_eps;
}
// Store which front we process (start with front 0) and the number of processed individuals.
unsigned int front_idx = 0;
unsigned int processed_individuals = 0;
// Vector for maintaining the original indices of points
std::vector<unsigned int> orig_indices;
while (processed_individuals < migration_rate) {
// If we need to pull every point from given front anyway, just push back the individuals right away
if (fronts_f[front_idx].size() <= (migration_rate - processed_individuals)) {
for(unsigned int i = 0 ; i < fronts_i[front_idx].size() ; ++i) {
result.push_back(pop.get_individual(fronts_i[front_idx][i]));
}
processed_individuals += fronts_f[front_idx].size();
++front_idx;
} else {
// Prepare the vector for the original indices
if (orig_indices.size() == 0) {
orig_indices.resize(fronts_i[front_idx].size());
iota(orig_indices.begin(), orig_indices.end(), 0);
}
// Compute the greatest contributor
hypervolume hv(fronts_f[front_idx], false);
hv.set_copy_points(false);
unsigned int gc_idx = hv.greatest_contributor(refpoint);
result.push_back(pop.get_individual(fronts_i[front_idx][orig_indices[gc_idx]]));
// Remove it from the front along with its index
orig_indices.erase(orig_indices.begin() + gc_idx);
fronts_f[front_idx].erase(fronts_f[front_idx].begin() + gc_idx);
++processed_individuals;
}
}
return result;
}
