A* with Lookahead Re-Evaluated

Zhaoxing Bu, Roni Stern, Ariel Felner, Robert C. Holte

Research output: Chapter in Book/Report/Conference proceedingConference contributionpeer-review

5 Scopus citations


A* with lookahead (AL*) is a variant of A* that performs a cost-bounded DFS lookahead from a node when it is generated. We show that the original version of AL* (AL 0) can, in some circumstances, fail to return an optimal solution because of the move pruning it does. We present two new versions, AL 1 and ELH, that we prove to always be correct and give conditions in which AL 0 is guaranteed to be correct. In our experiments with unit costs, AL 0 was usually the fastest AL* version, but its advantage was usually small. In our experiments with non-unit costs, AL 0 substantially outperforms both A* and IDA*. We also evaluate the idea of immediately expanding a generated node if it has the same f-value as its parent. We find that doing so causes AL* to require more memory and sometimes slows AL* down.

Original languageEnglish
Title of host publicationProceedings of the 7th Annual Symposium on Combinatorial Search, SoCS 2014
EditorsStefan Edelkamp, Roman Bartak
PublisherAAAI press
Number of pages9
ISBN (Electronic)9781577356769
StatePublished - 2014
Externally publishedYes
Event7th Annual Symposium on Combinatorial Search, SoCS 2014 - Prague, Czech Republic
Duration: 15 Aug 201417 Aug 2014

Publication series

NameProceedings of the 7th Annual Symposium on Combinatorial Search, SoCS 2014


Conference7th Annual Symposium on Combinatorial Search, SoCS 2014
Country/TerritoryCzech Republic

Bibliographical note

Publisher Copyright:
Copyright © 2014, Association for the Advancement of Artificial Intelligence (www.aaai.org). All rights reserved.


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