29,265 research outputs found
Flaw Selection Strategies for Partial-Order Planning
Several recent studies have compared the relative efficiency of alternative
flaw selection strategies for partial-order causal link (POCL) planning. We
review this literature, and present new experimental results that generalize
the earlier work and explain some of the discrepancies in it. In particular, we
describe the Least-Cost Flaw Repair (LCFR) strategy developed and analyzed by
Joslin and Pollack (1994), and compare it with other strategies, including
Gerevini and Schubert's (1996) ZLIFO strategy. LCFR and ZLIFO make very
different, and apparently conflicting claims about the most effective way to
reduce search-space size in POCL planning. We resolve this conflict, arguing
that much of the benefit that Gerevini and Schubert ascribe to the LIFO
component of their ZLIFO strategy is better attributed to other causes. We show
that for many problems, a strategy that combines least-cost flaw selection with
the delay of separable threats will be effective in reducing search-space size,
and will do so without excessive computational overhead. Although such a
strategy thus provides a good default, we also show that certain domain
characteristics may reduce its effectiveness.Comment: See http://www.jair.org/ for an online appendix and other files
accompanying this articl
Engineering a Conformant Probabilistic Planner
We present a partial-order, conformant, probabilistic planner, Probapop which
competed in the blind track of the Probabilistic Planning Competition in IPC-4.
We explain how we adapt distance based heuristics for use with probabilistic
domains. Probapop also incorporates heuristics based on probability of success.
We explain the successes and difficulties encountered during the design and
implementation of Probapop
On Guiding Search in HTN Temporal Planning with non Temporal Heuristics
The Hierarchical Task Network (HTN) formalism is used to express a wide
variety of planning problems as task decompositions, and many techniques have
been proposed to solve them. However, few works have been done on temporal HTN.
This is partly due to the lack of a formal and consensual definition of what a
temporal hierarchical planning problem is as well as the difficulty to develop
heuristics in this context. In response to these inconveniences, we propose in
this paper a new general POCL (Partial Order Causal Link) approach to represent
and solve a temporal HTN problem by using existing heuristics developed to
solve non temporal problems. We show experimentally that this approach is
performant and can outperform the existing ones
Plan stability: replanning versus plan repair
The ultimate objective in planning is to construct plans for execution. However, when a plan is executed in a real environment it can encounter differences between the expected and actual context of execution. These differences can manifest as divergences between the expected and observed states of the world, or as a change in the goals to be achieved by the plan. In both cases, the old plan must be replaced with a new one. In replacing the plan an important consideration is plan stability. We compare two alternative strategies for achieving the {em stable} repair of a plan: one is simply to replan from scratch and the other is to adapt the existing plan to the new context. We present arguments to support the claim that plan stability is a valuable property. We then propose an implementation, based on LPG, of a plan repair strategy that adapts a plan to its new context. We demonstrate empirically that our plan repair strategy achieves more stability than replanning and can produce repaired plans more efficiently than replanning
Towards a Reformulation Based Approach for Efficient Numeric Planning: Numeric Outer Entanglements
Restricting the search space has shown to be an effective approach for improving the performance of automated planning systems. A planner-independent technique for pruning the search space is domain and problem reformulation. Recently, Outer Entanglements, which are relations between planning operators and initial or goal predicates, have been introduced as a reformulation technique for eliminating potential undesirable instances of planning operators, and thus restricting the search space. Reformulation techniques, however,
have been mainly applied in classical planning, although many real-world planning applications require to deal with numerical information.
In this paper, we investigate the usefulness of reformulation approaches in planning with numerical fluents. In particular, we propose and extension of the notion of outer entanglements for handling numeric fluents. An empirical evaluation, which involves 150 instances from 5 domains, shows promising results
VAL : automatic plan validation, continuous effects and mixed initiative planning using PDDL
This paper describes aspects of our plan validation tool, VAL. The tool was initially developed to support the 3rd International Planning Competition, but has subsequently been extended in order to exploit its capabilities in plan validation and development. In particular, the tool has been extended to include advanced features of PDDL2.1 which have proved important in mixed-initiative planning in a space operations project. Amongst these features, treatment of continuous effects is the most significant, with important effects on the semantic interpretation of plans. The tool has also been extended to keep abreast of developments in PDDL, providing critical support to participants and organisers of the 4th IPC
Design and implementation of a Multi-Agent Planning System
This work introduces the design and implementation of a Multi-Agent Planning framework, in which a set of agents work jointly in order to devise a course of action to solve a certain planning problem.TorreƱo Lerma, A. (2011). Design and implementation of a Multi-Agent Planning System. http://hdl.handle.net/10251/15358Archivo delegad
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