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adding stubs to find fixed variables

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Signed-off-by: Nikolaj Bjorner <nbjorner@microsoft.com>
This commit is contained in:
Nikolaj Bjorner 2023-04-26 19:39:42 -07:00
parent ef943347ee
commit c48dc69050
3 changed files with 112 additions and 58 deletions
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55
src/math/lp/lar_solver.cpp
View file

@ -1382,11 +1382,62 @@ namespace lp {
// the lower/upper bound is not strict.
// the LP obtained by making the bound strict is infeasible
// -> the column has to be fixed
bool is_fixed_at_bound(column_index const& j) {
NOT_IMPLEMENTED_YET();
bool lar_solver::is_fixed_at_bound(column_index const& j) {
if (column_is_fixed(j))
return false;
mpq val;
if (!has_value(j, val))
return false;
lp::lconstraint_kind k;
if (column_has_upper_bound(j) &&
get_upper_bound(j).x == val) {
verbose_stream() << "check upper " << j << "\n";
push();
if (column_is_int(j))
k = LE, val -= 1;
else
k = LT;
auto ci = mk_var_bound(j, k, val);
update_column_type_and_bound(j, k, val, ci);
auto st = find_feasible_solution();
pop(1);
return st == lp_status::INFEASIBLE;
}
if (column_has_lower_bound(j) &&
get_lower_bound(j).x == val) {
verbose_stream() << "check lower " << j << "\n";
push();
if (column_is_int(j))
k = GE, val += 1;
else
k = GT;
auto ci = mk_var_bound(j, k, val);
update_column_type_and_bound(j, k, val, ci);
auto st = find_feasible_solution();
pop(1);
return st == lp_status::INFEASIBLE;
}
return false;
}
bool lar_solver::has_fixed_at_bound() {
verbose_stream() << "has-fixed-at-bound\n";
unsigned num_fixed = 0;
for (unsigned j = 0; j < A_r().m_columns.size(); ++j) {
auto ci = column_index(j);
if (is_fixed_at_bound(ci)) {
++num_fixed;
verbose_stream() << "fixed " << j << "\n";
}
}
verbose_stream() << "num fixed " << num_fixed << "\n";
if (num_fixed > 0)
find_feasible_solution();
return num_fixed > 0;
}
// below is the initialization functionality of lar_solver
bool lar_solver::strategy_is_undecided() const {

1
src/math/lp/lar_solver.h
View file

@ -367,6 +367,7 @@ public:
}
bool is_fixed_at_bound(column_index const& j);
bool has_fixed_at_bound();
bool is_fixed(column_index const& j) const { return column_is_fixed(j); }
inline column_index to_column_index(unsigned v) const { return column_index(external_to_column_index(v)); }