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https://github.com/Z3Prover/z3
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gomory cut worked on a toy example
Signed-off-by: Lev Nachmanson <levnach@microsoft.com>
This commit is contained in:
Lev Nachmanson
parent
94b3fee6ac
commit
4d1b0d8026
4 changed files with 104 additions and 62 deletions
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@ -213,7 +213,82 @@ void int_solver::int_case_in_gomory_cut(const mpq & a, unsigned x_j, mpq & k, la
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}
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}
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lia_move int_solver::mk_gomory_cut(lar_term& t, mpq& k, explanation & expl ) {
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lia_move int_solver::report_conflict_from_gomory_cut(mpq & k) {
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TRACE("empty_pol",
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display_row_info(tout,
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m_lar_solver->m_mpq_lar_core_solver.m_r_heading[m_gomory_cut_inf_column]););
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lp_assert(k.is_pos());
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// conflict 0 >= k where k is positive
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k.neg(); // returning 0 <= -k
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return lia_move::conflict;
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}
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void int_solver::gomory_cut_adjust_t_and_k_for_size_gt_1(
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vector<std::pair<mpq, unsigned>> & pol,
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lar_term & t,
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mpq &k,
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unsigned num_ints,
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mpq & lcm_den) {
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if (num_ints > 0) {
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lcm_den = lcm(lcm_den, denominator(k));
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TRACE("gomory_cut_detail", tout << "k: " << k << " lcm_den: " << lcm_den << "\n";
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linear_combination_iterator_on_vector<mpq> pi(pol);
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m_lar_solver->print_linear_iterator(&pi, tout);
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tout << "\nk: " << k << "\n";);
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lp_assert(lcm_den.is_pos());
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if (!lcm_den.is_one()) {
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// normalize coefficients of integer parameters to be integers.
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for (auto & pi: pol) {
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pi.first *= lcm_den;
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SASSERT(!is_int(pi.second) || pi.first.is_int());
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}
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k *= lcm_den;
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}
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TRACE("gomory_cut_detail", tout << "after *lcm_den\n";
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for (unsigned i = 0; i < pol.size(); i++) {
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tout << pol[i].first << " * v" << pol[i].second << "\n";
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}
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tout << "k: " << k << "\n";);
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}
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t.clear();
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// negate everything to return -pol <= -k
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for (const auto & pi: pol)
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t.add_monoid(-pi.first, pi.second);
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k.neg();
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}
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void int_solver::gomory_cut_adjust_t_and_k_for_size_1(const vector<std::pair<mpq, unsigned>> & pol, lar_term& t, mpq &k) {
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lp_assert(pol.size() == 1);
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unsigned j = pol[0].second;
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k /= pol[0].first;
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bool is_lower = pol[0].first.is_pos();
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if (is_int(j) && !k.is_int()) {
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k = is_lower?ceil(k):floor(k);
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}
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if (is_lower) { // returning -t <= -k which is equivalent to t >= k
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k.neg();
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t.negate();
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}
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}
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lia_move int_solver::report_gomory_cut(lar_term& t, mpq& k, mpq &lcm_den, unsigned num_ints) {
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lp_assert(!t.is_empty());
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auto pol = t.coeffs_as_vector();
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if (pol.size() == 1)
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gomory_cut_adjust_t_and_k_for_size_1(pol, t, k);
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else
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gomory_cut_adjust_t_and_k_for_size_gt_1(pol, t, k, num_ints, lcm_den);
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m_lar_solver->subs_terms_for_debugging(t); // todo: remove later
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return lia_move::cut;
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}
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lia_move int_solver::mk_gomory_cut(lar_term& t, mpq& k, explanation & expl) {
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lp_assert(column_is_int_inf(m_gomory_cut_inf_column));
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@ -238,59 +313,11 @@ lia_move int_solver::mk_gomory_cut(lar_term& t, mpq& k, explanation & expl ) {
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}
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}
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if (t.is_empty()) {
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TRACE("empty_pol",
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display_row_info(tout,
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m_lar_solver->m_mpq_lar_core_solver.m_r_heading[m_gomory_cut_inf_column]););
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lp_assert(k.is_pos());
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// conflict 0 >= k where k is positive
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k.neg(); // returning 0 <= -k
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return lia_move::conflict;
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}
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if (t.is_empty())
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return report_conflict_from_gomory_cut(k);
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auto pol = t.coeffs_as_vector();
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if (pol.size() == 1) {
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unsigned j = pol[0].second;
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k /= pol[0].first;
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bool is_lower = pol[0].first.is_pos();
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if (is_int(j) && !k.is_int()) {
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k = is_lower?ceil(k):floor(k);
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}
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if (is_lower) { // returning -t <= -k which is equivalent to t >= k
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k.neg();
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t.negate();
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}
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} else {
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if (num_ints > 0) {
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lcm_den = lcm(lcm_den, denominator(k));
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TRACE("gomory_cut_detail", tout << "k: " << k << " lcm_den: " << lcm_den << "\n";
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linear_combination_iterator_on_vector<mpq> pi(pol);
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m_lar_solver->print_linear_iterator(&pi, tout);
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tout << "\nk: " << k << "\n";);
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SASSERT(lcm_den.is_pos());
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if (!lcm_den.is_one()) {
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// normalize coefficients of integer parameters to be integers.
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for (auto & pi: pol) {
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pi.first *= lcm_den;
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SASSERT(!is_int(pi.second) || pi.first.is_int());
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}
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k *= lcm_den;
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}
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TRACE("gomory_cut_detail", tout << "after *lcm\n";
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for (unsigned i = 0; i < pol.size(); i++) {
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tout << pol[i].first << " * v" << pol[i].second << "\n";
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}
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tout << "k: " << k << "\n";);
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t.clear();
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// negate everything to return -pol <= -k
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for (const auto & pi: pol)
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t.add_monoid(-pi.first, pi.second);
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k.neg();
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} else {
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lp_assert(false); // not sure what happens here
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}
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}
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return lia_move::cut;
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return report_gomory_cut(t, k, lcm_den, num_ints);
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}
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void int_solver::init_check_data() {
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@ -370,6 +397,7 @@ lia_move int_solver::check(lar_term& t, mpq& k, explanation& ex) {
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if (st != lp_status::FEASIBLE && st != lp_status::OPTIMAL) {
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return lia_move::give_up;
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}
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init_inf_int_set(); // todo - can we avoid this call?
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int j = find_inf_int_base_column();
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if (j != -1) {
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// setup the call for gomory cut
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