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Both sides previous revision Previous revision Next revision | Previous revision Next revision Both sides next revision | ||
sav08:advanced_sat_solving_techniques [2008/03/12 21:40] vkuncak |
sav08:advanced_sat_solving_techniques [2008/03/13 10:49] vkuncak |
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Need efficient data structures: | Need efficient data structures: | ||
+ | * counters: simple, need many updates | ||
* head/tail list | * head/tail list | ||
- | * two-literal watching | + | * two-literal watching: each var has list of unassigned literals, do search to see if there are other literals to watch in clause |
+ | * invariant: each non-conflicting clause has at least one watched literal, but not all literals need to be watched | ||
+ | * no need to do anything on backtrack | ||
- | Other mechanisms less important: e.g. propagating equivalences. | + | Mechanisms other than unit propagation are less important: e.g. propagating equivalences. |
===== Conflict Analysis and Lemma Learning - analyze_conflict() ===== | ===== Conflict Analysis and Lemma Learning - analyze_conflict() ===== | ||
Line 85: | Line 88: | ||
If c1 is not asserting clause yet, we resolve it with antecedants of variables, following backwards deduction steps. | If c1 is not asserting clause yet, we resolve it with antecedants of variables, following backwards deduction steps. | ||
+ | |||
+ | In other words: we remove variables at current decision level until only one at the current is left. | ||
The clause forces a different value of a decision variable at a previous level. | The clause forces a different value of a decision variable at a previous level. |