Lifted Successor Generation in Numeric Planning

TL;DR

This paper introduces a novel lifted successor generator for numeric planning that efficiently handles numeric preconditions, reducing grounding size and supporting a broader class of planning problems.

Contribution

It extends a classical planning successor generator to support numeric preconditions, enabling more efficient lifted planning in numeric domains.

Findings

Supports numeric preconditions in lifted successor generation

Reduces exponential blowup in task representation

Achieves high applicability in benchmark domains

Abstract

Most planners ground numeric planning tasks, given in a first-order-like language, into a ground task representation. However, this can lead to an exponential blowup in task representation size, which occurs in practice for hard-to-ground tasks. We extend a state-of-the-art lifted successor generator for classical planning to support numeric precondition applicability. The method enumerates maximum cliques in a substitution consistency graph. Each maximum clique represents a substitution for the variables of the action schema, yielding a ground action. We augment this graph with numeric action preconditions and prove the successor generator is exact under formally specified conditions. When the conditions fail, our generator may list inapplicable ground actions; a final applicability check filters these without affecting completeness. However, this cannot happen in 23 of 25 benchmark domains, and it occurs only in 1 domain. To the authors' knowledge, no other lifted successor generator supports numeric action preconditions. This enables future research on lifted planning for a very rich planning fragment.