Computer Science – Discrete Mathematics
Scientific paper
2009-07-06
Computer Science
Discrete Mathematics
20 pages. Preliminary, conference versions of this article appeared in SAT08 and SAT09
Scientific paper
The QSAT problem is the quantified version of the SAT problem. We show the existence of a threshold effect for the phase transition associated with the satisfiability of random quantified extended 2-CNF formulas. We consider boolean CNF formulas of the form $\forall X \exists Y \varphi(X,Y)$, where $X$ has $m$ variables, $Y$ has $n$ variables and each clause in $\varphi$ has one literal from $X$ and two from $Y$. For such formulas, we show that the threshold phenomenon is controlled by the ratio between the number of clauses and the number $n$ of existential variables. Then we give the exact location of the associated critical ratio $c^{*}$. Indeed, we prove that $c^{*}$ is a decreasing function of $ \alpha$, where $\alpha$ is the limiting value of $m / \log (n)$ when $n$ tends to infinity.
Creignou Nadia
Daude Herve
Egly Uwe
Rossignol Raphael
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