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use fixed vars to explain tightening
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Signed-off-by: Lev Nachmanson <[email protected]>
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@levnach
levnach committed Feb 11, 2025
1 parent 36293ac commit 30f5599
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Showing 3 changed files with 55 additions and 41 deletions.
84 changes: 45 additions & 39 deletions src/math/lp/dioph_eq.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -372,6 +372,7 @@ namespace lp {

void subs_front_in_indexed_vector(std::queue<unsigned> & q) {
unsigned k = pop_front(q);
if (m_indexed_work_vector[k].is_zero()) return;
const eprime_entry& e = entry_for_subs(k);
TRACE("dioph_eq", tout << "k:" << k << ", in "; print_term_o(create_term_from_ind_c(), tout) << std::endl;
tout << "subs with e:"; print_eprime_entry(e, tout) << std::endl;);
Expand Down Expand Up @@ -557,7 +558,15 @@ namespace lp {
return false;
}
// g is not trivial, trying to tighten the bounds
return tighten_bounds_for_term(g, j);
// by using bitwise to explore both bounds
return tighten_bounds_for_term(g, j, true) | tighten_bounds_for_term(g, j, false);
}

void get_expl_from_meta_term(const lar_term& t, explanation& ex) {
for (const auto& p: t) {
const auto& l = lra.get_term(p.j());
get_expl_from_lar_term(l, ex);
}
}

void get_expl_from_lar_term(const lar_term & l, explanation& ex) {
Expand All @@ -580,13 +589,13 @@ namespace lp {
u_dependency *b_dep = nullptr;
if (lra.has_upper_bound(j, b_dep, rs, is_strict)) {
if (m_c > rs || (is_strict && m_c == rs)) {
get_expl_from_lar_term(m_tmp_l, m_infeas_explanation);
get_expl_from_meta_term(m_tmp_l, m_infeas_explanation);
return;
}
}
if (lra.has_lower_bound(j, b_dep, rs, is_strict)) {
if (m_c < rs || (is_strict && m_c == rs)) {
get_expl_from_lar_term(m_tmp_l, m_infeas_explanation);
get_expl_from_meta_term(m_tmp_l, m_infeas_explanation);
}
}
}
Expand All @@ -595,36 +604,25 @@ namespace lp {
// m_indexed_work_vector contains the coefficients of the term
// m_c contains the constant term
// m_tmp_l is the linear combination of the equations that removs the substituted variablse
bool tighten_bounds_for_term(const mpq& g, unsigned j) {
bool tighten_bounds_for_term(const mpq& g, unsigned j, bool is_upper) {
mpq rs;
bool is_strict;
bool change = false;
u_dependency *b_dep = nullptr;
SASSERT(!g.is_zero());

if (lra.has_upper_bound(j, b_dep, rs, is_strict)) {
if (lra.has_bound_of_type(j, b_dep, rs, is_strict, is_upper)) {
TRACE("dioph_eq", tout << "current upper bound for x:" << j << ":" << rs << std::endl;);
rs = (rs - m_c) / g;
TRACE("dioph_eq", tout << "(rs - m_c) / g:" << rs << std::endl;);
if (!rs.is_int()) {
tighten_bound_for_term_for_bound_kind(g, j, rs, true);
change = true;
}
}
if (lra.has_lower_bound(j, b_dep, rs, is_strict)) {
TRACE("dioph_eq", tout << "current lower bound for x" << j << ":" << rs << std::endl;);
rs = (rs - m_c) / g;
TRACE("dioph_eq", tout << "(rs - m_c) / g:" << rs << std::endl;);
if (!rs.is_int()) {
tighten_bound_for_term_for_bound_kind(g, j, rs, false);
change = true;
tighten_bound_for_term_for_bound_kind(g, j, rs, is_upper, b_dep);
return true;
}
}
return change;

return false;
}

void tighten_bound_for_term_for_bound_kind( const mpq& g, unsigned j, const mpq & ub, bool upper) {
void tighten_bound_for_term_for_bound_kind( const mpq& g, unsigned j, const mpq & ub, bool upper, u_dependency* prev_dep) {
// ub = (upper_bound(j) - m_c)/g.
// we have x[j] = t = g*t_+ m_c <= upper_bound(j), then
// t_ <= floor((upper_bound(j) - m_c)/g) = floor(ub)
Expand All @@ -638,42 +636,40 @@ namespace lp {

SASSERT(upper && bound < lra.get_upper_bound(j).x || !upper && bound > lra.get_lower_bound(j).x);
lconstraint_kind kind = upper? lconstraint_kind::LE: lconstraint_kind::GE;
u_dependency* dep = collect_explanation_from_indexed_vector(upper);
dep = lra.mk_join(dep, explain_fixed(m_tmp_l));
u_dependency* dep = prev_dep;
dep = lra.mk_join(dep, explain_fixed_in_meta_term(m_tmp_l));
u_dependency* j_bound_dep = upper? lra.get_column_upper_bound_witness(j): lra.get_column_lower_bound_witness(j);
dep = lra.mk_join(dep, j_bound_dep);
TRACE("dioph_eq", tout << "jterm:"; print_lar_term_L(lra.get_term(j), tout) << "\ndep:"; print_dep(tout, dep) << std::endl;);
lra.update_column_type_and_bound(j, kind, bound, dep);
}

u_dependency* explain_fixed(const lar_term& t) {
u_dependency* explain_fixed_in_meta_term(const lar_term& t) {
u_dependency* dep = nullptr;

for (const auto& p: t) {
if (is_fixed(p.j())) {
u_dependency* bound_dep = lra.get_bound_constraint_witnesses_for_column(p.j());
dep = lra.mk_join(dep, bound_dep);
lar_term const& term = lra.get_term(p.j());
for (const auto& q: term) {
if (is_fixed(q.j())) {
u_dependency* bound_dep = lra.get_bound_constraint_witnesses_for_column(q.j());
dep = lra.mk_join(dep, bound_dep);
}
}
}
return dep;
}

u_dependency* collect_explanation_from_indexed_vector(bool upper) {
TRACE("dioph_eq",
tout << (upper?"upper":"lower") << std::endl;
tout << "indexed_vec:"; print_term_o(create_term_from_ind_c(), tout);
);

term_o t = remove_fresh_vars(create_term_from_ind_c());

u_dependency* explain_fixed(const lar_term& t) {
u_dependency* dep = nullptr;
int bound_sign = upper? 1: -1;
for (const auto& p: t) {
int var_bound_sign = p.coeff().is_pos()? bound_sign: -bound_sign;
u_dependency* bound_dep = (var_bound_sign == 1? lra.get_column_upper_bound_witness(p.var()): lra.get_column_lower_bound_witness(p.var()));
dep = lra.mk_join(dep, bound_dep);
if (is_fixed(p.j())) {
u_dependency* bound_dep = lra.get_bound_constraint_witnesses_for_column(p.j());
dep = lra.mk_join(dep, bound_dep);
}
}
return dep;
}

public:
lia_move check() {
init();
Expand Down Expand Up @@ -916,7 +912,17 @@ namespace lp {
out << "\tm_l:{"; print_lar_term_L(e.m_l, out) << "}, ";
print_ml(e.m_l, out<< " \topened m_l:") << "\n";
}
out << "}\n";
switch (e.m_entry_status)
{
case entry_status::F:
out << "\tF\n";
break;
case entry_status::S:
out << "\tS\n";
break;
default:
out << "\tNOSF\n";
}
return out;
}

Expand Down
8 changes: 7 additions & 1 deletion src/math/lp/lar_solver.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1060,7 +1060,13 @@ namespace lp {
}
return ret;
}

bool lar_solver::has_bound_of_type(lpvar var, u_dependency*& ci, mpq& value, bool& is_strict, bool is_upper) const {
if (is_upper) {
return has_upper_bound(var, ci, value, is_strict);
} else {
return has_lower_bound(var, ci, value, is_strict);
}
}
bool lar_solver::has_lower_bound(lpvar var, u_dependency*& dep, mpq& value, bool& is_strict) const {

if (var >= m_columns.size()) {
Expand Down
4 changes: 3 additions & 1 deletion src/math/lp/lar_solver.h
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Original file line number Diff line number Diff line change
Expand Up @@ -510,7 +510,7 @@ class lar_solver : public column_namer {
u_dependency_manager& dep_manager() { return m_dependencies; }

inline u_dependency* get_column_upper_bound_witness(unsigned j) const {
return m_columns[j].upper_bound_witness();
return m_columns[j].upper_bound_witness();
}

inline const impq& get_upper_bound(lpvar j) const {
Expand All @@ -527,6 +527,8 @@ class lar_solver : public column_namer {

bool has_lower_bound(lpvar var, u_dependency*& ci, mpq& value, bool& is_strict) const;
bool has_upper_bound(lpvar var, u_dependency*& ci, mpq& value, bool& is_strict) const;
bool has_bound_of_type(lpvar var, u_dependency*& ci, mpq& value, bool& is_strict, bool is_upper) const;

bool has_value(lpvar var, mpq& value) const;
bool fetch_normalized_term_column(const lar_term& t, std::pair<mpq, lpvar>&) const;
bool column_is_fixed(unsigned j) const;
Expand Down

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