hv_greedy_s_policy.cpp

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#include <algorithm>
#include <vector>
#include <set>

#include "../population.h"
#include "base.h"
#include "base_s_policy.h"
#include "hv_greedy_s_policy.h"
#include "best_s_policy.h"
#include "../exceptions.h"
#include "../util/hypervolume.h"

using namespace pagmo::util;

namespace pagmo { namespace migration {


hv_greedy_s_policy::hv_greedy_s_policy(const double &rate, rate_type type, const double nadir_eps):base_s_policy(rate,type), m_nadir_eps(nadir_eps) { }

base_s_policy_ptr hv_greedy_s_policy::clone() const
{
        return base_s_policy_ptr(new hv_greedy_s_policy(*this));
}

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;
}

}}

BOOST_CLASS_EXPORT_IMPLEMENT(pagmo::migration::hv_greedy_s_policy)