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Strong Refutation Heuristics for Random k-SAT

Published online by Cambridge University Press:  14 August 2006

AMIN COJA-OGHLAN
Affiliation:
Humboldt-Universität zu Berlin, Institut für Informatik, Unter den Linden 6, 10099 Berlin, Germany (e-mail: coja@informatik.hu-berlin.de)
ANDREAS GOERDT
Affiliation:
Technische Universität Chemnitz, Fakultät für Informatik Straße der Nationen 62, 09107 Chemnitz, Germany (e-mail: goerdt@informatik.tu-chemnitz.de, lanka@informatik.tu-chemnitz.de)
ANDRÉ LANKA
Affiliation:
Technische Universität Chemnitz, Fakultät für Informatik Straße der Nationen 62, 09107 Chemnitz, Germany (e-mail: goerdt@informatik.tu-chemnitz.de, lanka@informatik.tu-chemnitz.de)
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Abstract

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A simple first moment argument shows that in a randomly chosen $k$-SAT formula with $m$ clauses over $n$ boolean variables, the fraction of satisfiable clauses is $1-2^{-k}+o(1)$ as $m/n\rightarrow\infty$ almost surely. In this paper, we deal with the corresponding algorithmic strong refutation problem: given a random $k$-SAT formula, can we find a certificate that the fraction of satisfiable clauses is $1-2^{-k}+o(1)$ in polynomial time? We present heuristics based on spectral techniques that in the case $k=3$ and $m\geq\ln(n)^6n^{3/2}$, and in the case $k=4$ and $m\geq Cn^2$, find such certificates almost surely. In addition, we present heuristics for bounding the independence number (resp. the chromatic number) of random $k$-uniform hypergraphs from above (resp. from below) for $k=3,4$.

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Paper
Copyright
© 2006 Cambridge University Press