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| 1 | +#include "cyclecut.h" |
| 2 | +#include "../pairwise/simple_methods.h" |
| 3 | + |
| 4 | +#include <iostream> |
| 5 | + |
| 6 | +// BEWARE: This does not handle equal rank or truncation! |
| 7 | +// TODO: FIX LATER. |
| 8 | +subelect_count_t get_triple_counts(const election_t & scores, |
| 9 | + const std::vector<bool> & hopefuls) { |
| 10 | + |
| 11 | + subelect_count_t counts; |
| 12 | + |
| 13 | + std::vector<size_t> involved_candidates(3); |
| 14 | + |
| 15 | + //std::cout << "Constructing triple counts...\n"; |
| 16 | + |
| 17 | + for (const ballot_group & bg: scores) { |
| 18 | + //std::cout << "New ballot, weight " << bg.get_weight() << "\n"; |
| 19 | + ordering::const_iterator cursor_a, cursor_b, cursor_c, |
| 20 | + end = bg.contents.end(); |
| 21 | + |
| 22 | + for (cursor_a = bg.contents.begin(); cursor_a != end; |
| 23 | + ++cursor_a) { |
| 24 | + |
| 25 | + if (!hopefuls[cursor_a->get_candidate_num()]) { |
| 26 | + continue; |
| 27 | + } |
| 28 | + |
| 29 | + for (cursor_b = cursor_a; cursor_b != end; ++cursor_b) { |
| 30 | + if (cursor_a == cursor_b) { |
| 31 | + continue; |
| 32 | + } |
| 33 | + if (!hopefuls[cursor_b->get_candidate_num()]) { |
| 34 | + continue; |
| 35 | + } |
| 36 | + if (cursor_a->get_score() == cursor_b->get_score()) { |
| 37 | + continue; |
| 38 | + } |
| 39 | + |
| 40 | + for (cursor_c = cursor_b; cursor_c != end; ++cursor_c) { |
| 41 | + if (cursor_b == cursor_c) { |
| 42 | + continue; |
| 43 | + } |
| 44 | + if (!hopefuls[cursor_c->get_candidate_num()]) { |
| 45 | + continue; |
| 46 | + } |
| 47 | + if (cursor_b->get_score() == cursor_c->get_score()) { |
| 48 | + continue; |
| 49 | + } |
| 50 | + |
| 51 | + involved_candidates[0] = cursor_a->get_candidate_num(); |
| 52 | + involved_candidates[1] = cursor_b->get_candidate_num(); |
| 53 | + involved_candidates[2] = cursor_c->get_candidate_num(); |
| 54 | + /*std::cout << "Updating "; |
| 55 | + std::copy(involved_candidates.begin(), involved_candidates.end(), |
| 56 | + std::ostream_iterator<size_t>(std::cout, " ")); |
| 57 | + std::cout << "\n";*/ |
| 58 | + std::sort(involved_candidates.begin(), |
| 59 | + involved_candidates.end()); |
| 60 | + |
| 61 | + // Set a_idx to the index of the highest ranked candidate |
| 62 | + // in the involved candidates vector after sorting. |
| 63 | + // (Just go through the vector to find the index. |
| 64 | + // Quick and dirty.) |
| 65 | + size_t a_idx = 0; |
| 66 | + while (involved_candidates[a_idx] != |
| 67 | + cursor_a->get_candidate_num()) { |
| 68 | + ++a_idx; |
| 69 | + } |
| 70 | + |
| 71 | + subelect_count_t::iterator sc_pos = |
| 72 | + counts.find(involved_candidates); |
| 73 | + |
| 74 | + if (sc_pos == counts.end()) { |
| 75 | + std::vector<double> unit_count(3, 0); |
| 76 | + unit_count[a_idx] = bg.get_weight(); |
| 77 | + |
| 78 | + counts[involved_candidates] = unit_count; |
| 79 | + } else { |
| 80 | + sc_pos->second[a_idx] += bg.get_weight(); |
| 81 | + } |
| 82 | + } |
| 83 | + } |
| 84 | + } |
| 85 | + } |
| 86 | + |
| 87 | + return counts; |
| 88 | +} |
| 89 | + |
| 90 | +// cycle_fpa_fpc |
| 91 | + |
| 92 | +cycle_fpa_fpc::cycle_fpa_fpc(const std::vector<size_t> & cycle_in, |
| 93 | + const subelect_count_t & subelect_count) { |
| 94 | + |
| 95 | + cycle = cycle_in; |
| 96 | + std::vector<size_t> sorted_cycle = cycle; |
| 97 | + std::sort(sorted_cycle.begin(), sorted_cycle.end()); |
| 98 | + |
| 99 | + std::vector<double> first_prefs = subelect_count.find( |
| 100 | + sorted_cycle)->second; |
| 101 | + |
| 102 | + // Now descramble the count-order so it's in cycle order |
| 103 | + // instead of sorted candidate order. (Yeah, this is ugly.) |
| 104 | + |
| 105 | + std::vector<double> cycle_order_fpps(3); |
| 106 | + for (size_t i = 0; i < 3; ++i) { |
| 107 | + for (size_t j = 0; j < 3; ++j) { |
| 108 | + if (sorted_cycle[i] == cycle[j]) { |
| 109 | + cycle_order_fpps[j] = first_prefs[i]; |
| 110 | + } |
| 111 | + } |
| 112 | + } |
| 113 | + |
| 114 | + /*std::cout << "Adding cycle "; |
| 115 | + std::copy(cycle_in.begin(), cycle_in.end(), std::ostream_iterator<size_t>(std::cout, " ")); |
| 116 | + std::cout << " with first prefs "; |
| 117 | + std::copy(cycle_order_fpps.begin(), cycle_order_fpps.end(), std::ostream_iterator<double>(std::cout, " ")); |
| 118 | + std::cout << "\n";*/ |
| 119 | + |
| 120 | + fpA_fpC_score = cycle_order_fpps[0] - cycle_order_fpps[2]; |
| 121 | +} |
| 122 | + |
| 123 | +// Cycle-cutting |
| 124 | + |
| 125 | +bool cycle_cutting::is_cycle(const condmat & matrix, |
| 126 | + const std::vector<size_t> & c) const { |
| 127 | + |
| 128 | + return matrix.beats(c[0], c[1]) && matrix.beats(c[1], c[2]) && |
| 129 | + matrix.beats(c[2], c[0]); |
| 130 | + |
| 131 | +} |
| 132 | + |
| 133 | +std::pair<ordering, bool> cycle_cutting::elect_inner( |
| 134 | + const election_t & papers, |
| 135 | + const std::vector<bool> & hopefuls, |
| 136 | + int num_candidates, cache_map * cache, |
| 137 | + bool winner_only) const { |
| 138 | + |
| 139 | + size_t numcands = num_candidates; // HACK |
| 140 | + |
| 141 | + // First get the Condorcet matrix and triple subelection count. |
| 142 | + condmat matrix(papers, num_candidates, CM_WV); |
| 143 | + subelect_count_t subelect_count = get_triple_counts( |
| 144 | + papers, hopefuls); |
| 145 | + |
| 146 | + // non-neutrality test. HACK |
| 147 | + for (size_t a = 0; a < numcands; ++a) { |
| 148 | + for (size_t b = a+1; b < numcands; ++b) { |
| 149 | + if (matrix.get_magnitude(a, b) == matrix.get_magnitude(b, a)) { |
| 150 | + matrix.add(a, b, 1e-5); |
| 151 | + } |
| 152 | + } |
| 153 | + } |
| 154 | + |
| 155 | + // Then determine what three-candidate cycles exist, and for each |
| 156 | + // of these cycles, insert the cycle, and the fpA-fpC score of the |
| 157 | + // first candidate in that cycle for the subelection containing |
| 158 | + // only the cycle members. |
| 159 | + |
| 160 | + std::vector<size_t> cycle(3); |
| 161 | + std::vector<cycle_fpa_fpc> cycle_scores; |
| 162 | + |
| 163 | + for (cycle[0] = 0; cycle[0] < numcands; ++cycle[0]) { |
| 164 | + if (!hopefuls[cycle[0]]) { |
| 165 | + continue; |
| 166 | + } |
| 167 | + |
| 168 | + for (cycle[1] = 0; cycle[1] < numcands; ++cycle[1]) { |
| 169 | + if (cycle[0] == cycle[1] || !hopefuls[cycle[1]]) { |
| 170 | + continue; |
| 171 | + } |
| 172 | + |
| 173 | + for (cycle[2] = 0; cycle[2] < numcands; ++cycle[2]) { |
| 174 | + if (cycle[0] == cycle[2] || cycle[1] == cycle[2] || |
| 175 | + !hopefuls[cycle[2]]) { |
| 176 | + continue; |
| 177 | + } |
| 178 | + |
| 179 | + /*std::cout << "Checking if this is a cycle: "; |
| 180 | + std::copy(cycle.begin(), cycle.end(), std::ostream_iterator<size_t>(std::cout, " ")); |
| 181 | + std::cout << "\n";*/ |
| 182 | + |
| 183 | + // We only care about cycles. |
| 184 | + if (!is_cycle(matrix, cycle)) { |
| 185 | + continue; |
| 186 | + } |
| 187 | + |
| 188 | + cycle_scores.push_back(cycle_fpa_fpc( |
| 189 | + cycle, subelect_count)); |
| 190 | + } |
| 191 | + } |
| 192 | + } |
| 193 | + |
| 194 | + // Sort the list in descending order, and for each member of the list, |
| 195 | + // check if there's still a cycle. If so, break the cycle at the edge |
| 196 | + // pointing to the fpA-fpC winner. |
| 197 | + |
| 198 | + std::sort(cycle_scores.begin(), cycle_scores.end(), std::greater<>()); |
| 199 | + |
| 200 | + for (const cycle_fpa_fpc & cur_cycle: cycle_scores) { |
| 201 | + // Check if it's still a cycle, since earlier cycle-breaking |
| 202 | + // might have broken this cycle too. |
| 203 | + if (!is_cycle(matrix, cur_cycle.cycle)) { |
| 204 | + continue; |
| 205 | + } |
| 206 | + |
| 207 | + // Break the cycle between the last and first candidate. |
| 208 | + matrix.set(cur_cycle.cycle[2], cur_cycle.cycle[0], 0); |
| 209 | + } |
| 210 | + |
| 211 | + // Once all of that is done, hand the modified matrix to a Condorcet |
| 212 | + // method and return its outcome. |
| 213 | + |
| 214 | + return ord_minmax(CM_WV).pair_elect(matrix, |
| 215 | + hopefuls, cache, winner_only); |
| 216 | +} |
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