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sav08:advanced_sat_solving_techniques [2008/03/12 21:34] vkuncak |
sav08:advanced_sat_solving_techniques [2008/03/13 10:43] vkuncak |
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| Line 45: | Line 45: | ||
| 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 clause has at least one watched literal, but not all literals need to be watched | ||
| - | 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 66: | Line 68: | ||
| analyze_conflict() { | analyze_conflict() { | ||
| cl = find_conflicting_clause(); | cl = find_conflicting_clause(); | ||
| - | while (!stop_criterion_met(c1)) { | + | while (!is_asserting_clause(c1)) { |
| var = var_of_lit(choose_literal(c1)); | var = var_of_lit(choose_literal(c1)); | ||
| c1 = resolve(c1, antecedant(var), var); | c1 = resolve(c1, antecedant(var), var); | ||
| Line 79: | Line 81: | ||
| * deduction rule was that some original clause C became unit clause because all literals exept literal containing var were false | * deduction rule was that some original clause C became unit clause because all literals exept literal containing var were false | ||
| * then antecedant(var) is C | * then antecedant(var) is C | ||
| + | |||
| + | asserting clause: | ||
| + | * false at current decision level | ||
| + | * only one literal has current decision level (others were assigned before) | ||
| + | |||
| + | If c1 is not asserting clause yet, we resolve it with antecedants of variables, following backwards deduction steps. | ||
| + | |||
| + | The clause forces a different value of a decision variable at a previous level. | ||
| ===== Storing Clauses ===== | ===== Storing Clauses ===== | ||