
| Planner    | Solved   | Attempted   | Success ratio   |
|------------|----------|-------------|-----------------|
| LPG        | 42       | 468         | 94%             |
| FF         | 237      | 284         | 83%             |
| 91         | 122      | 75%         |                 |
| Simplanner |          |             |                 |
| Sapa       | 80       | 122         | 6%              |
| MIPS       | 31       | 508         | 65%             |
| VHP OP     | 1 22     | 224         | 54%             |
| Stella     | 50       | 102         | 49%             |
| TP4        | 26       | 204         | 13%             |
| TP SYS     | 14       | 1 20        | 12%             |
| SemSyn     | 11       | 144         | 8%              |

Table 1: Number of problems attempted and solved by the planners that took part in the 3rd IPC ordered by their success ratio. The data from the planners compared with LPG are from the official web site of the 3rd IPC. The data for LPG do not consider the 20 problems in Satellite HardNumeric, which are all solved by the current version of the planner, slightly improving the success ratio.

ssse many problems could not be solved due to a minor bug in the parser of our planner that was easily fixed right after the competition.

Overall, the number of problems attempted in the new tests by our planner was 468
(over a total of 508 problems), and the success ratio was 94.4% (the problems attempted by LPG in the competition were 428 and the success ratio 87%). Figure 1 gives these data for every fully-automated planner that took part in the competition. The success ratio of LPG is the highest one over all competing domain-independent planners.

The version of LPG that we used in the competition is integrated with an alternative search method that can be activated when the local search is not effective. This method is based on the same best-first search technique implemented in FF (Hoffinann & Nebel, 2001).

The only domain were we used best-first search instead of local search is FreeCells . The 40 problems that were not attempted by our planner are the 20 problems in Settlers Numeric and the 20 problems in Satellite HardNumeric. The first domain contains operators with universally quantified effects, which are not handled in the current version of LPG. The plan metrics of the problems in the second domain require maximizing the value of a certain numerical variable representing acquired data ( data-stored ), which is another feature of PDDL2.1 that the competition version of LPG did not handle properly. Many of these problems were solved by the other fully-automated planners by the empty plan or by plans with zero quality. While such plans could have been derived also by LPG, we did not consider these interesting solutions. 23