Keywords: classical planning, heuristic search, shortest cost-optimal planning
TL;DR: We consider the problem of finding a shortest cost-optimal plan, suggest various solutions based on cost-algebraic A* and on cost transformation with standard A*, and empirically compare these suggested solutions.
Abstract: 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 cost-optimal plans, one corresponding to an instantiation of cost-algebraic 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.