HARRIS: Hybrid Ranking and Regression Forests for Algorithm Selection
It is well known that different algorithms perform differently well on an
instance of an algorithmic problem, motivating algorithm selection (AS): Given
an instance of an algorithmic problem, which is the most suitable algorithm to
solve it? As such, the AS problem has received considerable attention resulting
in various approaches - many of which either solve a regression or ranking
problem under the hood. Although both of these formulations yield very natural
ways to tackle AS, they have considerable weaknesses. On the one hand,
correctly predicting the performance of an algorithm on an instance is a
sufficient, but not a necessary condition to produce a correct ranking over
algorithms and in particular ranking the best algorithm first. On the other
hand, classical ranking approaches often do not account for concrete
performance values available in the training data, but only leverage rankings
composed from such data. We propose HARRIS- Hybrid rAnking and RegRessIon
foreSts - a new algorithm selector leveraging special forests, combining the
strengths of both approaches while alleviating their weaknesses. HARRIS'
decisions are based on a forest model, whose trees are created based on splits
optimized on a hybrid ranking and regression loss function. As our preliminary
experimental study on ASLib shows, HARRIS improves over standard algorithm
selection approaches on some scenarios showing that combining ranking and
regression in trees is indeed promising for AS.