Reusing Comparator Networks in Pseudo-Boolean Encodings

A Pseudo-Boolean (PB) constraint is a linear inequality constraint over Boolean literals. One of the popular, efficient ideas used to solve PB-problems (a set of PB-constraints) is to translate them to SAT instances (encodings) via, for example, sorting networks, then to process those instances using state-of-the-art SAT-solvers. In this paper we show an improvement of such technique. By using a variation of a greedy set cover algorithm, when adding constraints to our encoding, we reuse parts of the already encoded PB-instance in order to decrease the size (the number of variables and clauses) of the resulting SAT instance. The experimental evaluation shows that the proposed method increases the number of solved instances.