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backjumping/notes

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This commit is contained in:
Jakob Rath 2022-09-19 16:43:11 +02:00
parent a416e16566
commit 806571d2cd
2 changed files with 25 additions and 13 deletions
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31
src/math/polysat/conflict2.cpp
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@ -124,6 +124,9 @@ namespace polysat {
// TODO: apply conflict resolution plugins here too?
} else {
VERIFY(s.m_viable.resolve(v, *this));
// TODO: in general the forbidden interval lemma is not asserting.
// but each branch exclude the current assignment.
// in those cases we will (additionally?) need an abstraction that is asserting to make sure viable is updated properly.
set_backjump();
logger().begin_conflict("forbidden interval lemma");
}
@ -140,7 +143,7 @@ namespace polysat {
if (c.is_always_true())
return;
LOG("Inserting: " << c);
SASSERT(!c.is_always_false()); // if we add c, the core would be a tautology
SASSERT(!c.is_always_false()); // if we added c, the core would be a tautology
SASSERT(!c->vars().empty());
m_literals.insert(c.blit().index());
for (pvar v : c->vars()) {
@ -176,7 +179,6 @@ namespace polysat {
m_var_occurrences[v]--;
}
void conflict2::resolve_bool(sat::literal lit, clause const& cl) {
// Note: core: x, y, z; corresponds to clause ~x \/ ~y \/ ~z
// clause: x \/ u \/ v
@ -202,25 +204,25 @@ namespace polysat {
SASSERT(contains(lit));
SASSERT(!contains(~lit));
if (is_backjumping())
return;
unsigned const lvl = s.m_bvars.level(lit);
signed_constraint c = s.lit2cnstr(lit);
/*
// TODO: why bail_vars?
// If evaluation depends on a decision,
// then we rather keep the more general constraint c instead of inserting "x = v"
bool has_decision = false;
for (pvar v : c->vars())
if (s.is_assigned(v) && s.m_justification[v].is_decision())
m_bail_vars.insert(v), has_decision = true;
if (!has_decision) {
remove(c);
for (pvar v : c->vars())
if (s.is_assigned(v) && s.get_level(v) <= lvl)
m_vars.insert(v);
}
*/
remove(c);
for (pvar v : c->vars())
if (s.is_assigned(v) && s.get_level(v) <= lvl)
m_vars.insert(v);
logger().log(inf_resolve_with_assignment(s, lit, c));
}
@ -228,13 +230,20 @@ namespace polysat {
bool conflict2::resolve_value(pvar v) {
SASSERT(contains_pvar(v));
if (is_backjumping()) {
for (auto const& c : s.m_viable.get_constraints(v))
for (pvar v : c->vars())
logger().log_var(v);
return false;
}
if (is_bailout())
return false;
auto const& j = s.m_justification[v];
// if (j.is_decision() && m_bail_vars.contains(v))
// return false;
if (j.is_decision() && m_bail_vars.contains(v)) // TODO: what if also m_vars.contains(v)? might have a chance at elimination
return false;
s.inc_activity(v);
m_vars.remove(v);

7
src/math/polysat/conflict2.h
View file

@ -76,6 +76,7 @@ TODO:
- may force backjumping without further conflict resolution (e.g., if applicable lemma was found by global analysis of search state)
- bailout lemma if no method applies (log these cases in particular because it indicates where we are missing something)
- force a restart if we get a bailout lemma or non-asserting conflict?
- consider case if v is both in vars and bail_vars (do we need to keep it in bail_vars even if we can eliminate it from vars?)
--*/
@ -100,6 +101,7 @@ namespace polysat {
// bailout lemma because no appropriate conflict resolution method applies
bailout,
// force backjumping without further conflict resolution because a good lemma has been found
// TODO: distinguish backtrack/revert of last decision from backjump to second-highest level in the lemma
backjump,
};
@ -110,11 +112,12 @@ namespace polysat {
// current conflict core consists of m_literals and m_vars
indexed_uint_set m_literals; // set of boolean literals in the conflict
uint_set m_vars; // variable assignments used as premises, shorthand for literals (x := v)
// uint_set m_bail_vars; // tracked for cone of influence but not directly involved in conflict resolution
uint_set m_bail_vars; // tracked for cone of influence but not directly involved in conflict resolution
unsigned_vector m_var_occurrences; // for each variable, the number of constraints in m_literals that contain it
// additional lemmas generated during conflict resolution
// TODO: we might not need all of these in the end. add only the side lemmas which justify a constraint in the final lemma (recursively)?
vector<clause_ref> m_lemmas;
conflict2_kind_t m_kind = conflict2_kind_t::ok;
@ -141,7 +144,7 @@ namespace polysat {
bool contains(signed_constraint c) const { SASSERT(c); return contains(c.blit()); }
bool contains(sat::literal lit) const;
bool contains_pvar(pvar v) const { return m_vars.contains(v) /* || m_bail_vars.contains(v) */; }
bool contains_pvar(pvar v) const { return m_vars.contains(v) || m_bail_vars.contains(v); }
/**
* Insert constraint c into conflict state.