Transition Landmarks from Abstraction Cuts

Florian Pommerening, Clemens Büchner, Thomas Keller

Keywords: classical planning, operator counting, abstraction heuristics, landmarks

TL;DR: Transition-counting constraints are a principled tool to formalize constraints and can be used to express landmarks obtained from cuts in abstractions.

Abstract: We introduce *transition-counting constraints* as a principled tool to formalize constraints that must hold in every solution of a transition system. We show how to obtain *transition landmark* constraints from *abstraction cuts*. Transition landmarks dominate operator landmarks in theory but require solving a linear program that is prohibitively large in practice. We compare different approximations that replace transition-counting variables with more compact operator-counting variables. These are based on projections to operator landmarks and further relaxations. For one important special case, we show that the projection is lossless even for integer-valued variables. We finally discuss efficient data structures to derive cuts from abstractions and store them in a way that avoids repeated computation in every state. We compare the resulting heuristics and other heuristics both theoretically and on the IPC benchmarks.

Category: Long

Student: No

Submission Number: 265