What Makes The Difference Between HSP and FF?

The HSP and FF systems are state-of-the-art domain independent planners. FF can historically be seen as a successor of HSP. It is based on the same ideas like HSP, but differs from its predecessor in a number of details. FF outperforms HSP in many planning domains. We have carried out a large scale experiment where we ran all configurations of FF's new techniques on a sizeable set of planning tasks. We describe the experimental design, and present our findings. The results give a clear picture of what the most important reasons are for FF's performance advantage over HSP.