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8.6  Comparison to other Planners

In this section, we present comparative results between the Grt planner and other planners. We decided to use Hsp-2 (Bonet & Geffner, 2001), Ff (Hoffman & Nebel, 2001), Stan (Long & Fox, 2000; Fox & Long, 2000, 2001) and Altalt (Nigenda, Nguyen & Kambhampati, 2000)[1]. All these planners took part in the domain independent track of the Aips-00 planning competition. We selected these planners because Hsp-2 and Stan are state-of–the-art planning systems, Ff has been awarded for its outstanding performance in the last competition and Altalt is a new but very promising domain-independent state-space heuristic planner.

The aim of our experiments is to have an overall view of the performance of the evaluated systems. Performing pair wise comparisons between specific optimization techniques is not possible, since these techniques are implemented on top of different systems. Moreover, this kind of comparisons is out of the scope of this paper, which focuses in the use of specific directions for constructing the heuristic and traversing the space of the states, in the area of domain-independent heuristic state-space planning, and not in the evaluation of the numerous pre-processing optimization techniques. However, in the cases where we identify the contribution of a specific feature in the performance of a planner, we comment on this.

In order to have fair comparisons, we used exactly the same problem and domain description files for all planners. So, Grt ran without XOR-constraints or numerical representation of resources. Moreover, although the irrelevant object elimination technique is an integral feature of Grt, it had no contribution in these domains, since there were not irrelevant objects. We believe that the absence of irrelevant objects in these domains does not mean that this technique has limited applicability, but it is an indication that more real domains for testing purposes have to be used in the future, since the planning tasks in our real-life are full of irrelevant objects. Finally, the domain enrichment technique proved valuable for the elevator domain only. However, this technique, as well as the goal enhancement one, has not to be seen as an optimization technique, but as a way to overcome the problems that arise from the backward direction of the heuristic construction.

We tested the planners in several domains taken from the planning competitions and from the literature, in the same workstation and within the 5 minutes time limit. The results are presented in the following.

 

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Ioannis Refanidis

14-8-2001

 



[1]   Stan is available at http://www.dur.ac.uk/~dcs0www/research/stanstuff/stanpage.html
Ff is available at http://www.informatik.uni-freiburg.de/~hoffmann/ff.html
Hsp-2 is available at http://www.ldc.usb.ve/~hector/
Altalt is available at http://rakaposhi.eas.asu.edu/altweb/altalt.html