A clause-based heuristic for SAT solvers

Nachum Dershowitz*, Ziyad Hanna, Alexander Nadel

*Corresponding author for this work

Research output: Contribution to journalConference articlepeer-review


We propose a new decision heuristic for DPLL-based propositional SAT solvers. Its essence is that both the initial and the conflict clauses are arranged in a list and the next decision variable is chosen from the top-most unsatisfied clause. Various methods of initially organizing the list and moving the clauses within it are studied. Our approach is an extension of one used in Berkmin, and adopted by other modern solvers, according to which only conflict clauses are organized in a list, and a literal-scoring-based secondary heuristic is used when there are no more unsatisfied conflict clauses. Our approach, implemented in the 2004 version of zChaff solver and in a generic Chaff-based SAT solver, results in a significant performance boost on hard industrial bench-marks.

Original languageEnglish
Pages (from-to)46-60
Number of pages15
JournalLecture Notes in Computer Science
StatePublished - 2005
Event8th International Conference on Theory and Applications of Satisfiability Testing, SAT 2005 - St Andrews, United Kingdom
Duration: 19 Jun 200523 Jun 2005


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