Solving optimal satisfiability problems through clause-directed A*
Name
51589373-MIT.pdf
Description
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Author(s)
Ragno, Robert J. (Robert John), 1977-
Advisor(s)
Brian C. Williams.
Alternative Title
Solving optimal satisfiability problems through ClA*
Date Issued
2002
Publisher
Massachusetts Institute of Technology
Abstract
Real-world applications, such as diagnosis and embedded control, are increasingly being framed as OpSAT problems - problems of finding the best solution that satisfies a formula in propositional state logic. Previous methods, such as Conflict-directed A*, solve OpSAT problems through a weak coupling of A* search, used to generate optimal candidates, and a DPLL-based SAT solver, used to test feasibility. This paper achieves a substantial performance improvement by introducing a tightly coupled approach, Clause-directed A * (CIA *). ClA* simultaneously directs the search towards assignments that are feasible and optimal. First, satisfiability is generalized to state logic by unifying the DPLL satisfiability procedure with forward checking. Second, optimal assignments are found by using A* to guide variable splitting within DPLL. Third, search is directed towards feasible regions of the state space by treating all clauses as conflicts, and by selecting only assignments that entail more clauses. Finally, ClA* climbs towards the optimum by using a variable ordering heuristic that emulates gradient search. Empirical experiments on real-world and randomly-generated instances demonstrate an order of magnitude increase in performance over Conflict-directed A*.
Description
Thesis (M.Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2002.
Includes bibliographical references (p. 37-38).
Subjects
Electrical Engineering and Computer Science.
MIT Department
Massachusetts Institute of Technology. Department of Electrical Engineering and Computer Science
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