Abstract. We study the set of solutions of random k-satisfiability formulas through the cavity method. It is known that, for an interval of the clause-to-variables ratio, this decomposes into an exponential number of pure states (clusters). We refine substantially this picture by: (i) determining the precise location of the clustering transition; (ii) uncovering a second 'condensation' phase transition in the structure of the solution set for k≥4. These results both follow from computing the large deviation rate of the internal entropy of pure states. From a technical point of view our main contributions are a simplified version of the cavity formalism for special values of the Parisi replica symmetry breaking parameter m (in particular for m = 1 via a correspondence with the tree reconstruction problem) and new large-k expansions.

Key words: cavity and replica method; disordered systems (theory); message-passing algorithms; random graphs, networks

Received 29 February 2008, accepted for publication 12 March 2008
Published 8 April 2008