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Add propagate/narrow for ule_constraint (#5214)

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* Add helper to check whether pdd is univariate and linear

* Reorganize propagate/narrow of eq_constraint

* Implement propagate/narrow for ule constraints

* Also push trail instruction in push_viable
This commit is contained in:
Jakob Rath 2021-04-23 17:41:02 +02:00 • committed by GitHub
parent 12444c7e8b
commit 2fac9e6e66
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6 changed files with 111 additions and 51 deletions
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72
src/math/polysat/eq_constraint.cpp
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@ -36,39 +36,9 @@ namespace polysat {
return true;
}
}
LOG("Assignments: " << s.m_search);
auto q = p().subst_val(s.m_search);
LOG("Substituted: " << p() << " := " << q);
TRACE("polysat", tout << p() << " := " << q << "\n";);
if (q.is_zero())
return false;
if (q.is_never_zero()) {
LOG("Conflict (never zero under current assignment)");
s.set_conflict(*this);
return false;
}
// at most one variable remains unassigned.
auto other_var = vars()[1 - idx];
SASSERT(!q.is_val() && q.var() == other_var);
// Detect and apply unit propagation.
if (try_narrow_with(q, s)) {
rational val;
switch (s.find_viable(other_var, val)) {
case dd::find_t::empty:
s.set_conflict(*this);
return false;
case dd::find_t::singleton:
s.propagate(other_var, val, *this);
return false;
case dd::find_t::multiple:
/* do nothing */
break;
}
}
narrow(s);
return false;
}
@ -89,31 +59,37 @@ namespace polysat {
return nullptr;
}
bool eq_constraint::try_narrow_with(pdd const& q, solver& s) {
if (q.is_linear() && q.free_vars().size() == 1) {
void eq_constraint::narrow(solver& s) {
LOG("Assignment: " << s.m_search);
auto q = p().subst_val(s.m_search);
LOG("Substituted: " << p() << " := " << q);
if (q.is_zero())
return;
if (q.is_never_zero()) {
LOG("Conflict (never zero under current assignment)");
s.set_conflict(*this);
return;
}
if (q.is_unilinear()) {
// a*x + b == 0
pvar v = q.var();
rational a = q.hi().val();
rational b = q.lo().val();
bddv const& x = s.var2bits(v).var();
bdd xs = (a * x + b == rational(0));
s.intersect_viable(v, xs);
s.push_cjust(v, this);
return true;
}
// TODO: what other constraints can be extracted cheaply?
return false;
}
s.intersect_viable(v, xs);
void eq_constraint::narrow(solver& s) {
// NSB code review:
// This should also use the current assignment so be similar to propagate.
// The idea is that narrow is invoked when the constraint is first added
// and also when the constraint is used in a conflict.
// When it is used in a conflict, there could be a partial assignment in s.m_search
// that fixes variables in p().
//
(void)try_narrow_with(p(), s);
rational val;
if (s.find_viable(v, val) == dd::find_t::singleton) {
s.propagate(v, val, *this);
}
return;
}
// TODO: what other constraints can be extracted cheaply?
}
bool eq_constraint::is_always_false() {