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; }