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add optional feature to bound search within ranges

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Signed-off-by: Nikolaj Bjorner <nbjorner@microsoft.com>
This commit is contained in:
Nikolaj Bjorner 2020-06-14 21:34:54 -07:00
parent 180fb3abf6
commit 395a304262
5 changed files with 129 additions and 6 deletions
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1
src/smt/params/smt_params_helper.pyg
View file

@ -75,6 +75,7 @@ def_module_params(module_name='smt',
('arith.auto_config_simplex', BOOL, False, 'force simplex solver in auto_config'),
('arith.rep_freq', UINT, 0, 'the report frequency, in how many iterations print the cost and other info'),
('arith.min', BOOL, False, 'minimize cost'),
('arith.bounded_expansion', BOOL, False, 'box variables used in branch and bound into bound assumptions'),
('arith.print_stats', BOOL, False, 'print statistic'),
('arith.simplex_strategy', UINT, 0, 'simplex strategy for the solver'),
('arith.enable_hnf', BOOL, True, 'enable hnf (Hermite Normal Form) cuts'),

2
src/smt/params/theory_arith_params.cpp
View file

@ -38,6 +38,7 @@ void theory_arith_params::updt_params(params_ref const & _p) {
m_arith_reflect = p.arith_reflect();
m_arith_eager_eq_axioms = p.arith_eager_eq_axioms();
m_arith_auto_config_simplex = p.arith_auto_config_simplex();
m_arith_bounded_expansion = p.arith_bounded_expansion();
arith_rewriter_params ap(_p);
m_arith_eq2ineq = ap.eq2ineq();
@ -78,6 +79,7 @@ void theory_arith_params::display(std::ostream & out) const {
DISPLAY_PARAM(m_arith_adaptive_gcd);
DISPLAY_PARAM(m_arith_propagation_threshold);
DISPLAY_PARAM(m_arith_pivot_strategy);
DISPLAY_PARAM(m_arith_bounded_expansion);
DISPLAY_PARAM(m_arith_add_binary_bounds);
DISPLAY_PARAM(m_arith_propagation_strategy);
DISPLAY_PARAM(m_arith_eq_bounds);

3
src/smt/params/theory_arith_params.h
View file

@ -82,6 +82,8 @@ struct theory_arith_params {
bool m_arith_adaptive_gcd;
unsigned m_arith_propagation_threshold;
bool m_arith_bounded_expansion;
arith_pivot_strategy m_arith_pivot_strategy;
// used in diff-logic
@ -139,6 +141,7 @@ struct theory_arith_params {
m_arith_eager_gcd(false),
m_arith_adaptive_gcd(false),
m_arith_propagation_threshold(UINT_MAX),
m_arith_bounded_expansion(false),
m_arith_pivot_strategy(ARITH_PIVOT_SMALLEST),
m_arith_add_binary_bounds(false),
m_arith_propagation_strategy(ARITH_PROP_PROPORTIONAL),

125
src/smt/theory_lra.cpp
View file

@ -932,7 +932,11 @@ public:
m_solver(nullptr),
m_resource_limit(*this),
m_farkas("farkas"),
m_bp(*this)
m_bp(*this),
m_bounded_range_idx(0),
m_bounded_range_lit(null_literal),
m_bound_predicates(m),
m_bound_predicate(m)
{
}
@ -1769,7 +1773,13 @@ public:
}
// create a bound atom representing term >= k is lower_bound is true, and term <= k if it is false
app_ref mk_bound(lp::lar_term const& term, rational const& k, bool lower_bound) {
rational offset = k;
rational offset;
expr_ref t(m);
return mk_bound(term, k, lower_bound, offset, t);
}
app_ref mk_bound(lp::lar_term const& term, rational const& k, bool lower_bound, rational& offset, expr_ref& t) {
offset = k;
u_map<rational> coeffs;
term2coeffs(term, coeffs);
bool is_int = true;
@ -1815,7 +1825,7 @@ public:
// tout << "offset: " << offset << " gcd: " << g << "\n";);
app_ref atom(m);
app_ref t = coeffs2app(coeffs, rational::zero(), is_int);
t = coeffs2app(coeffs, rational::zero(), is_int);
if (lower_bound) {
atom = a.mk_ge(t, a.mk_numeral(offset, is_int));
}
@ -2056,7 +2066,9 @@ public:
app_ref b(m);
bool u = m_lia->is_upper();
auto const & k = m_lia->get_offset();
b = mk_bound(m_lia->get_term(), k, !u);
rational offset;
expr_ref t(m);
b = mk_bound(m_lia->get_term(), k, !u, offset, t);
if (m.has_trace_stream()) {
app_ref body(m);
body = m.mk_or(b, m.mk_not(b));
@ -2071,6 +2083,7 @@ public:
// SAT core assigns a value to
lia_check = l_false;
++m_stats.m_branch;
add_variable_bound(t, offset);
break;
}
case lp::lia_move::cut: {
@ -3874,6 +3887,100 @@ public:
st.update("arith-assume-eqs", m_stats.m_assume_eqs);
st.update("arith-branch", m_stats.m_branch);
}
/*
* Facility to put a small box around integer variables used in branch and bounds.
*/
struct bound_info {
rational m_offset;
unsigned m_range;
bound_info() {}
bound_info(rational const& o, unsigned r):m_offset(o), m_range(r) {}
};
unsigned m_bounded_range_idx; // current size of bounded range.
literal m_bounded_range_lit; // current bounded range literal
expr_ref_vector m_bound_predicates; // predicates used for bounds
expr_ref m_bound_predicate;
obj_map<expr, expr*> m_predicate2term;
obj_map<expr, bound_info> m_term2bound_info;
bool use_bounded_expansion() const {
return ctx().get_fparams().m_arith_bounded_expansion;
}
unsigned init_range() const { return 5; }
unsigned max_range() const { return 20; }
void add_theory_assumptions(expr_ref_vector& assumptions) {
if (!use_bounded_expansion())
return;
ctx().push_trail(value_trail<context, literal>(m_bounded_range_lit));
m_bound_predicate = m.mk_fresh_const("arith.bound", m.mk_bool_sort());
m_bounded_range_lit = mk_literal(m_bound_predicate);
// add max-unfolding literal
// add variable bounds
assumptions.push_back(m_bound_predicate);
for (auto const& kv : m_term2bound_info) {
bound_info const& bi = kv.m_value;
expr* t = kv.m_key;
expr_ref hi(a.mk_le(t, a.mk_int(bi.m_offset + bi.m_range)), m);
expr_ref lo(a.mk_ge(t, a.mk_int(bi.m_offset - bi.m_range)), m);
assumptions.push_back(lo);
assumptions.push_back(hi);
IF_VERBOSE(10, verbose_stream() << lo << "\n" << hi << "\n");
}
}
bool should_research(expr_ref_vector& unsat_core) {
if (!use_bounded_expansion())
return false;
bool found = false;
expr* t = nullptr;
for (auto & e : unsat_core) {
if (e == m_bound_predicate) {
found = true;
for (auto & kv : m_term2bound_info)
if (kv.m_value.m_range == init_range())
kv.m_value.m_range *= 2;
}
else if (m_predicate2term.find(e, t)) {
found = true;
bound_info bi;
VERIFY(m_term2bound_info.find(t, bi));
if (bi.m_range >= max_range()) {
m_term2bound_info.erase(t);
}
else {
bi.m_range *= 2;
m_term2bound_info.insert(t, bi);
}
}
}
return found;
}
void add_variable_bound(expr* t, rational const& offset) {
if (!use_bounded_expansion())
return;
if (m_bounded_range_lit == null_literal)
return;
// if term is not already bounded, add a range and assert max_bound => range
bound_info bi(offset, init_range());
if (m_term2bound_info.find(t, bi))
return;
expr_ref hi(a.mk_le(t, a.mk_int(offset + bi.m_range)), m);
expr_ref lo(a.mk_ge(t, a.mk_int(offset - bi.m_range)), m);
mk_axiom(~m_bounded_range_lit, mk_literal(hi));
mk_axiom(~m_bounded_range_lit, mk_literal(lo));
m_bound_predicates.push_back(lo);
m_bound_predicates.push_back(hi);
IF_VERBOSE(10, verbose_stream() << "add " << lo << " " << hi << "\n");
m_predicate2term.insert(lo, t);
m_predicate2term.insert(hi, t);
m_term2bound_info.insert(t, bi);
}
};
theory_lra::theory_lra(context& ctx):
@ -3888,8 +3995,7 @@ theory* theory_lra::mk_fresh(context* new_ctx) {
}
void theory_lra::init() {
m_imp->init();
}
}
bool theory_lra::internalize_atom(app * atom, bool gate_ctx) {
return m_imp->internalize_atom(atom, gate_ctx);
}
@ -3997,6 +4103,13 @@ theory_var theory_lra::add_objective(app* term) {
expr_ref theory_lra::mk_ge(generic_model_converter& fm, theory_var v, inf_rational const& val) {
return m_imp->mk_ge(fm, v, val);
}
void theory_lra::add_theory_assumptions(expr_ref_vector& assumptions) {
m_imp->add_theory_assumptions(assumptions);
}
bool theory_lra::should_research(expr_ref_vector& unsat_core) {
return m_imp->should_research(unsat_core);
}
}
template class lp::lp_bound_propagator<smt::theory_lra::imp>;
template void lp::lar_solver::propagate_bounds_for_touched_rows<smt::theory_lra::imp>(lp::lp_bound_propagator<smt::theory_lra::imp>&);

4
src/smt/theory_lra.h
View file

@ -95,6 +95,10 @@ namespace smt {
void collect_statistics(::statistics & st) const override;
void add_theory_assumptions(expr_ref_vector& assumptions) override;
bool should_research(expr_ref_vector& unsat_core) override;
// optimization
expr_ref mk_ge(generic_model_converter& fm, theory_var v, inf_rational const& val);
inf_eps value(theory_var) override;