Section: New Results

B&BGrid revisited for solving challenging Q3AP instances on large volatile computational environments

Participants : Nouredine Melab, El-Ghazali Talbi.

We have revisited the design and implementation of parallel B&B algorithms on multi-core (collaboration with UMONS, Belgium) and grid-wide environments (collaboration with University of Luxembourg and UMONS, Belgium)) for solving to otimality and efficiently large permutation problem instances. We have proposed a gridification approach of the B&B algorithm called B&B@Grid. This later includes a dynamic load balancing technique and a checkpointing mechanism for permutation problems. The approach has been validated through single-permutation Flowshop problem. In [23] , we have extended the approach to deal with more than one permutation. To do that, we have revisited the design and implementation of the dynamic load balancing and checkpointing mechanisms for multiple permutation-problems. The new approach allowed the optimal resolution on a nation-wide grid (Grid'5000) of a difficult instance of the 3D quadratic assignment problem (Q3AP). To solve the instance, an average of 1,123 processing cores were used during less than 12 days with a peak of around 3,427 CPU cores.