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a simple version of choosing a column for gomory cut

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This commit is contained in:
Lev Nachmanson 2023-12-04 15:06:50 -10:00
parent f98b42ae42
commit fc23a498c4
6 changed files with 90 additions and 96 deletions
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64
src/math/lp/gomory.cpp
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@ -409,73 +409,15 @@ lia_move gomory::cut(lar_term & t, mpq & k, explanation* ex, unsigned basic_inf_
create_cut cc(t, k, ex, basic_inf_int_j, row, lia);
return cc.cut();
}
bool gomory::is_gomory_cut_target(const row_strip<mpq>& row) {
// All non base variables must be at their bounds and assigned to rationals (that is, infinitesimals are not allowed).
unsigned j;
for (const auto & p : row) {
j = p.var();
if (!lia.is_base(j) && (!lia.at_bound(j) || !is_zero(lia.get_value(j).y))) {
TRACE("gomory_cut", tout << "row is not gomory cut target:\n";
lia.display_column(tout, j);
tout << "infinitesimal: " << !is_zero(lia.get_value(j).y) << "\n";);
return false;
}
}
return true;
}
int gomory::find_basic_var() {
unsigned n = 0;
int result = -1;
unsigned min_row_size = UINT_MAX;
#if 1
result = lia.select_int_infeasible_var(true);
if (result == -1)
return result;
TRACE("gomory_cut", tout << "row: " << result << "\n");
const row_strip<mpq>& row = lra.get_row(lia.row_of_basic_column(result));
if (is_gomory_cut_target(row))
return result;
result = -1;
UNREACHABLE();
#endif
for (unsigned j : lra.r_basis()) {
if (!lia.column_is_int_inf(j))
continue;
const row_strip<mpq>& row = lra.get_row(lia.row_of_basic_column(j));
TRACE("gomory_cut", tout << "try j" << j << "\n");
if (!is_gomory_cut_target(row))
continue;
IF_VERBOSE(20, lia.display_row_info(verbose_stream(), lia.row_of_basic_column(j)));
// Prefer smaller row size
if (min_row_size == UINT_MAX ||
2*row.size() < min_row_size ||
(4*row.size() < 5*min_row_size && lia.random() % (++n) == 0)) {
result = j;
n = 1;
min_row_size = std::min(min_row_size, row.size());
}
}
return result;
}
lia_move gomory::operator()() {
int j = find_basic_var();
if (j == -1)
return lia_move::undef;
lia_move gomory::get_cut(lpvar j) {
unsigned r = lia.row_of_basic_column(j);
const row_strip<mpq>& row = lra.get_row(r);
SASSERT(lra.row_is_correct(r));
SASSERT(is_gomory_cut_target(row));
SASSERT(lia.is_gomory_cut_target(j));
lia.m_upper = false;
lia.m_cut_vars.push_back(j);
return cut(lia.m_t, lia.m_k, lia.m_ex, j, row);
return cut(lia.m_t, lia.m_k, lia.m_ex, j, row);
}