On Producing Shortest Cost-Optimal Plans

Cost-optimal planning is at the heart of planning research, with many existing planners that produce provably optimal solutions. While some applications pose additional restrictions, such as producing shortest (in the number of actions) among the cost-optimal plans, standard cost-optimal planning does not provide such a guarantee. We discuss two possible approaches to produce provably the shortest among the costoptimal plans, one corresponding to an instantiation of costalgebraic A∗, the other based on a cost transformation. We formally prove that the new cost-transformation method indeed produces the shortest among the cost-optimal plans and empirically compare the performance of the approaches in different configurations.