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A Randomized Algorithm for 3-SAT

A Randomized Algorithm for 3-SAT In this work we propose and analyze a simple randomized algorithm for 3-SAT (i.e. an algorithm to find a satisfiable assignment for a Boolean formula in conjunctive normal form (CNF) having at most 3 literals in every clause). Given a k-CNF formula $${\phi}$$ on n variables, and $${\alpha \in \{0,1\}^n}$$ that satisfies $${\phi}$$ , a clause of $${\phi}$$ is critical if exactly one literal of that clause is satisfied under assignment α. Paturi et al. (Chicago J. Theor. Comput. Sci. 115, 1999) proposed a simple randomized algorithm (PPZ) for k-SAT for which success probability increases with the number of critical clauses (with respect to a fixed satisfiable solution of the input formula). Here, we first describe another simple randomized algorithm DEL which performs better if the number of critical clauses in input formula are less (with respect to a fixed satisfiable solution of the input formula). Subsequently, we combine these two simple algorithms such that the success probability of the combined algorithm is maximum of the success probabilities of PPZ and DEL on every input instance. We show that when the average number of clauses for a variable that appear as unique true literals in one or more critical clauses in $${\phi}$$ is between 1 and 2/(3 · log (3/2)), combined algorithm performs better than the PPZ algorithm. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Mathematics in Computer Science Springer Journals

A Randomized Algorithm for 3-SAT

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References (31)

Publisher
Springer Journals
Copyright
Copyright © 2010 by Birkhäuser / Springer Basel AG
Subject
Mathematics; Mathematics, general; Computer Science, general
ISSN
1661-8270
eISSN
1661-8289
DOI
10.1007/s11786-010-0036-3
Publisher site
See Article on Publisher Site

Abstract

In this work we propose and analyze a simple randomized algorithm for 3-SAT (i.e. an algorithm to find a satisfiable assignment for a Boolean formula in conjunctive normal form (CNF) having at most 3 literals in every clause). Given a k-CNF formula $${\phi}$$ on n variables, and $${\alpha \in \{0,1\}^n}$$ that satisfies $${\phi}$$ , a clause of $${\phi}$$ is critical if exactly one literal of that clause is satisfied under assignment α. Paturi et al. (Chicago J. Theor. Comput. Sci. 115, 1999) proposed a simple randomized algorithm (PPZ) for k-SAT for which success probability increases with the number of critical clauses (with respect to a fixed satisfiable solution of the input formula). Here, we first describe another simple randomized algorithm DEL which performs better if the number of critical clauses in input formula are less (with respect to a fixed satisfiable solution of the input formula). Subsequently, we combine these two simple algorithms such that the success probability of the combined algorithm is maximum of the success probabilities of PPZ and DEL on every input instance. We show that when the average number of clauses for a variable that appear as unique true literals in one or more critical clauses in $${\phi}$$ is between 1 and 2/(3 · log (3/2)), combined algorithm performs better than the PPZ algorithm.

Journal

Mathematics in Computer ScienceSpringer Journals

Published: Apr 16, 2010

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