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Add BDD utilities; use them for narrowing/propagation of linear equality constraints (#5192)

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* Add a few helper methods for encoding sets of integers as BDDs

* Use BDD functions in solver

* Add bdd::find_int

* Use bdd::find_int in solver

* Add narrowing for linear equality constraints

* Simplify code for linear propagation

* Add test for later

* Narrowing can only handle linear constraints with a single variable

* Need to push_cjust
This commit is contained in:
Jakob Rath 2021-04-16 17:44:18 +02:00 • committed by GitHub
parent e970fe5034
commit f72e30e539
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10 changed files with 208 additions and 104 deletions
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47
src/math/polysat/solver.cpp
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@ -30,44 +30,23 @@ namespace polysat {
}
bool solver::is_viable(pvar v, rational const& val) {
bdd b = m_viable[v];
for (unsigned k = size(v); k-- > 0 && !b.is_false(); )
b &= val.get_bit(k) ? m_bdd.mk_var(k) : m_bdd.mk_nvar(k);
return !b.is_false();
return m_viable[v].contains_int(val, size(v));
}
void solver::add_non_viable(pvar v, rational const& val) {
LOG("pvar " << v << " /= " << val);
TRACE("polysat", tout << "v" << v << " /= " << val << "\n";);
bdd value = m_bdd.mk_true();
for (unsigned k = size(v); k-- > 0; )
value &= val.get_bit(k) ? m_bdd.mk_var(k) : m_bdd.mk_nvar(k);
SASSERT((value && !m_viable[v]).is_false());
push_viable(v);
m_viable[v] &= !value;
SASSERT(is_viable(v, val));
intersect_viable(v, !m_bdd.mk_int(val, size(v)));
}
lbool solver::find_viable(pvar v, rational & val) {
val = 0;
bdd viable = m_viable[v];
if (viable.is_false())
return l_false;
bool is_unique = true;
unsigned num_vars = 0;
while (!viable.is_true()) {
++num_vars;
if (!viable.lo().is_false() && !viable.hi().is_false())
is_unique = false;
if (viable.lo().is_false()) {
val += rational::power_of_two(viable.var());
viable = viable.hi();
}
else
viable = viable.lo();
}
is_unique &= num_vars == size(v);
TRACE("polysat", tout << "v" << v << " := " << val << " unique " << is_unique << "\n";);
return is_unique ? l_true : l_undef;
void solver::intersect_viable(pvar v, bdd vals) {
push_viable(v);
m_viable[v] &= vals;
}
dd::find_int_t solver::find_viable(pvar v, rational & val) {
return m_viable[v].find_int(size(v), val);
}
@ -312,15 +291,15 @@ namespace polysat {
IF_LOGGING(log_viable(v));
rational val;
switch (find_viable(v, val)) {
case l_false:
case dd::find_int_t::empty:
LOG("Conflict: no value for pvar " << v);
set_conflict(v);
break;
case l_true:
case dd::find_int_t::singleton:
LOG("Propagation: pvar " << v << " := " << val << " (due to unique value)");
assign_core(v, val, justification::propagation(m_level));
break;
case l_undef:
case dd::find_int_t::multiple:
LOG("Decision: pvar " << v << " := " << val);
push_level();
assign_core(v, val, justification::decision(m_level));