- Description by author: AltAlt started out as "a little of this, and a little of that". It is a student-only effort where a group of graduate students parallely toyed with a number of alternative planning ideas and evaluated them before fielding the better one. The actual idea used in the competition, GP-HSP, which became the official AltAlt planner, uses effective and admissible heuristics extracted from the planning graph to drive the backward state space search. AltAlt was developed in Lisp and later ported to C for the competition (round1). A problem we faced was that the relatively newer C version was hard to try better heuristics with, as the competition progressed, even when newer heuristics were easily seen to be feasible in the Lisp version.
- Publications
- Source Code: Remote, Local
- Platform: Red Hat Linux 6.0
- Input Language: PDDL
- Implementation Language: C & Lisp
- See Also: Graph-based planners
- Description by author: FF (Fast-Forward) is basically a variation
of HSP. Interpreting the HSP heuristic as a special case of the graph building
phase in GRAPHLAN, it extends the heuristic to also employ GRAPHPLAN's plan
extraction phase. The length of the plans that GRAPHPLAN returns give a
heuristic goal distance measure, and the actions that GRAPHPLAN selects can
be used for guiding search.
Using these informations, FF employs a novel local search strategy that combines Hill-climbing with systematic search. It makes use of the fact that phenomena like big plateaus or local minima — with respect to the heuristic described above — do not occur very often in benchmark planning problems.
Metric-FF is an extension of the FF planner to (ADL combined with) numerical state variables, more precisely to PDDL 2.1 level 2, yet more precisely to the subset of PDDL 2.1 level 2 with the algorithmic principles.
-
-
Publications:
- J. Hoffmann, B. Nebel, The FF Planning System: Fast Plan Generation Through Heuristic Search, in: Journal of Artificial Intelligence Research, Volume 14, 2001, Pages 253 - 302.
- J. Hoffmann, FF: The Fast-Forward Planning System, in: AI Magazine, Volume 22, Number 3, 2001, Pages 57 - 62.
- J. Hoffmann, The Metric-FF Planning System: Translating ``Ignoring Delete Lists'' to Numerical State Variables, submitted to: Journal of Artificial Intelligence Research, special issue on the 3rd International Planning Competition.
- Input Language: PDDL, PDDL2.1 &ADL
- Implementation Language: C
- See Also: Graph-based planners
HSP2.0 descends from the HSP planner. The idea
is similar: planning instances are mapped into state-space search problems
that are solved with heuristics extracted from the representation.
Unlike the original HSP planner, the new version supports forward and
backward search, several heuristics, and a more expressive modeling
language (a fragment of typed ADL). The search algorithm is Weighted A*;
an A* search with the heuristic multiplied by a constant W > 1.
There are also a number of improvements in the code.
Different options (search direction/heuristic) can be run in sequence or
concurrently.
Publications
Publications:
