Restricted Path Consistency Revisited

Restricted path consistency (RPC) is a strong local consistency for binary constraints that was proposed 20 years ago and was identified as a promising alternative to arc consistency (AC) in an early experimental study of local consistencies for binary constraints. However, and in contrast to other strong local consistencies such as SAC and maxRPC, it has been neglected since then. In this paper we revisit RPC. First, we propose RPC3, a new lightweight RPC algorithm that is very easy to implement and can be efficiently applied throughout search. Then we perform a wide experimental study of RPC3 and a light version that achieves an approximation of RPC, comparing them to state-of-theart AC and maxRPC algorithms. Experimental results clearly show that restricted RPC is by far more efficient than both AC and maxRPC when applied throughout search. These results strongly suggest that it is time to reconsider the established perception that MAC is the best general purpose method for solving binary CSPs.