public function watch2OnHighest(Decisions $decisions)
{
$literals = $this->rule->getLiterals();
if ($literals < 3) {
return;
}
$watchLevel = 0;
foreach ($literals as $literal) {
$level = $decisions->decisionLevel($literal);
if ($level > $watchLevel) {
$this->watch2 = $literal;
$watchLevel = $level;
}
}
}
/**
* Places the second watch on the rule's literal, decided at the highest level
*
* Useful for learned rules where the literal for the highest rule is most
* likely to quickly lead to further decisions.
*
* @param Decisions $decisions The decisions made so far by the solver
*/
public function watch2OnHighest(Decisions $decisions)
{
$literals = $this->rule->getLiterals();
// if there are only 2 elements, both are being watched anyway
if ($literals < 3) {
return;
}
$watchLevel = 0;
foreach ($literals as $literal) {
$level = $decisions->decisionLevel($literal);
if ($level > $watchLevel) {
$this->watch2 = $literal;
$watchLevel = $level;
}
}
}
/**
* Propagates a decision on a literal to all rules watching the literal
*
* If a decision, e.g. +A has been made, then all rules containing -A, e.g.
* (-A|+B|+C) now need to satisfy at least one of the other literals, so
* that the rule as a whole becomes true, since with +A applied the rule
* is now (false|+B|+C) so essentially (+B|+C).
*
* This means that all rules watching the literal -A need to be updated to
* watch 2 other literals which can still be satisfied instead. So literals
* that conflict with previously made decisions are not an option.
*
* Alternatively it can occur that a unit clause results: e.g. if in the
* above example the rule was (-A|+B), then A turning true means that
* B must now be decided true as well.
*
* @param int $decidedLiteral The literal which was decided (A in our example)
* @param int $level The level at which the decision took place and at which
* all resulting decisions should be made.
* @param Decisions $decisions Used to check previous decisions and to
* register decisions resulting from propagation
* @return Rule|null If a conflict is found the conflicting rule is returned
*/
public function propagateLiteral($decidedLiteral, $level, $decisions)
{
// we invert the decided literal here, example:
// A was decided => (-A|B) now requires B to be true, so we look for
// rules which are fulfilled by -A, rather than A.
$literal = -$decidedLiteral;
if (!isset($this->watchChains[$literal])) {
return null;
}
$chain = $this->watchChains[$literal];
$chain->rewind();
while ($chain->valid()) {
$node = $chain->current();
$otherWatch = $node->getOtherWatch($literal);
if (!$node->getRule()->isDisabled() && !$decisions->satisfy($otherWatch)) {
$ruleLiterals = $node->getRule()->getLiterals();
$alternativeLiterals = array_filter($ruleLiterals, function ($ruleLiteral) use($literal, $otherWatch, $decisions) {
return $literal !== $ruleLiteral && $otherWatch !== $ruleLiteral && !$decisions->conflict($ruleLiteral);
});
if ($alternativeLiterals) {
reset($alternativeLiterals);
$this->moveWatch($literal, current($alternativeLiterals), $node);
continue;
}
if ($decisions->conflict($otherWatch)) {
return $node->getRule();
}
$decisions->decide($otherWatch, $level, $node->getRule());
}
$chain->next();
}
return null;
}
