On the strength of time-indexed formulations for the resource-constrained project scheduling problem

For non-preemptive scheduling, time-indexed zero-one linear programming formulations have been deeply analyzed. This note clarifies the current knowledge about the strength of these formulations and shows that some formulations that have been proposed “new” in the literature are in fact weaker or equivalent to those already known. Much of the arguments used follow from a Ph.D. thesis by Sousa, which has been largely overlooked in the literature.