The Algorithm Selection Competitions 2015 and 2017
  The algorithm selection problem is to choose the most suitable algorithm for
solving a given problem instance. It leverages the complementarity between
different approaches that is present in many areas of AI. We report on the
state of the art in algorithm selection, as defined by the Algorithm Selection
competitions in 2015 and 2017. The results of these competitions show how the
state of the art improved over the years. We show that although performance in
some cases is very good, there is still room for improvement in other cases.
Finally, we provide insights into why some scenarios are hard, and pose
challenges to the community on how to advance the current state of the art.
