Browsing by Author "Ikonen, Eetu"

The maximum constraint satisfaction problem (MaxCSP) is a combinatorial optimization problem in which the set of feasible solutions is expressed using decision variables and constraints on how the variables can be assigned. It can be used to represent a wide range of other combinatorial optimization problems. The maximum satisfiability problem (MaxSAT) is a restricted variant of the maximum constraint satisfaction problem with the additional restrictions that all variables must be Boolean variables, and all constraints must be logical Boolean formulas. Because of this, expressing problems using MaxSAT can be unintuitive. The known solving methods for the MaxSAT problem are more efficient than the known solving methods for MaxCSP. Therefore, it is desirable to express problems using MaxSAT. However, every MaxCSP instance that only has finite-domain variables can be encoded into an equivalent MaxSAT instance. Encoding a MaxCSP instance to a MaxSAT instance allows users to combine the strengths of both approaches by expressing problems using the more intuitive MaxCSPs but solving them using the more efficient MaxSAT solving methods. In this thesis, we overview three common MaxCSP to MaxSAT encodings, the sparse, log, and order encodings, that differ in how they encode an integer variable into a set of Boolean variables. We use correlation clustering as a practical example for comparing the encodings. We first represent correlation clustering problems using MaxCSPs, and then encode them into MaxSATs instances. State-of-the-art MaxSAT solvers are then used to solve the MaxSAT instances. We compare the encodings by measuring the time it takes to encode a MaxCSP instance into a MaxSAT instance and the time it takes to solve the MaxSAT instance. The scope of our experiments is too small to draw general conclusions but in our experiments, the log encoding was the best overall choice.