SUNNY-CP and the MiniZinc Challenge

In Constraint Programming (CP) a portfolio solver combines a variety of different constraint solvers for solving a given problem. This fairly recent approach enables to significantly boost the performance of single solvers, especially when multicore architectures are exploited. In this work we give a brief overview of the portfolio solver sunny-cp, and we discuss its performance in the MiniZinc Challenge---the annual international competition for CP solvers---where it won two gold medals in 2015 and 2016. Under consideration in Theory and Practice of Logic Programming (TPLP)Comment: Under consideration in Theory and Practice of Logic Programming (TPLP

Parallelizing Constraint Solvers for Hard RCPSP Instances

The Resource-Constrained Project Scheduling Problem (RCPSP) is a well-known scheduling problem aimed at minimizing the makespan of a project subject to temporal and resource constraints. Constraint Programming allows to model and solve RCPSPs in a natural and efficient way, especially when Lazy Clause Generation (LCG) techniques are employed. In this paper we show that hard RCPSPs can be efficiently tackled by a portfolio approach that combines the strengths of different —not necessarily LCG-based— solvers by exploiting their parallel execution on multiple cores. Our approach seeks to predict and run the best solvers for a new, unseen RCPSP instance and also enables the bounds communication between them. This on-average allows to outperform the oracle solver that always chooses the best available solver for any given instance