CHARACTERIZATION AND GENERATION OF A GENERAL-CLASS OF RESOURCE-CONSTRAINED PROJECT SCHEDULING PROBLEMS

This paper addresses the issue of how to generate problem instances of controlled difficulty. It focuses on precedence- and resource-constra ined (project) scheduling problems, but similar ideas may be applied t o other network optimization problems. It describes a network construc tion procedure that takes into account a) constraints on the network t opology, b) a resource factor that reflects the density of the coeffic ient matrix, and c) a resource strength, which measures the availabili ty of resources. The strong impact of the chosen parametric characteri zation of the problems is shown via an in depth computational study. I nstances for the single- and multi-mode resource-constrained project s cheduling problem are benchmarked by using the state of the art (branc h and bound) procedures. The results provided, demonstrate that the cl assical benchmark instances used by several researchers over decades b elong to the subset of the very easy ones. In addition, it is shown th at hard instances, being far more smaller in size than presumed in the literature, may not be solved to optimality even within a large amoun t of computation time.