Loop Detection in the PANDA Planning System
| HTN planning loop detection graph search |
PaperID: 49
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| The International Planning Competition (IPC) in 2020 was the first one for a long time to host tracks on Hierarchical Task Network (HTN) planning. HyperTensioN, the winner of the tack on totally ordered problems, comes with an interesting technique: it stores parts of the decomposition path in the state to mark expanded tasks and forces its depth first search to leave recursive structures in the hierarchy. This can be seen as a form of loop detection (LD) -- a technique that is not very common in HTN planning. This might be due to the spirit of encoding enough advice in the model to find plans (so that loop detection is simply not necessary), or because it becomes a computationally hard task in the general (i.e. partially ordered) setting. We integrated several (approximate and exact) techniques for LD into the heuristic progression search of the HTN planning system PANDA. We test our new techniques on the benchmark set of the IPC 2020. Both in the partially ordered (PO) and totally ordered (TO) track, PANDA with LD beats the winners of the competition. In the PO setting, our LD techniques increase the lead in comparison to the IPC systems. In the TO setting, PANDA is placed 3rd place without our LD techniques, but 1st when using it. | |
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