Anomalies in parallel branch-and-bound algorithms

Abstract

We consider the effects of parallelizing branch-and-bound algorithms by expanding several live nodes simultaneously. It is shown that it is quite possible for a parallel branch-and-bound algorithm using n 2 processors to take more time than one using n 1 processors, even though n 1 < n 2 . Furthermore, it is also possible to achieve speed-ups that are in excess of the ratio n 2 / n 1 . Experimental results with the 0 / 1-Knapsack and Traveling Salesman problems are also presented.