{"type":"ScholarlyArticle","title":"Front-to-End Bidirectional Heuristic Search with Near-Optimal Node Expansions","authors":[{"name":"Jingwei Chen","slug":"jingwei-chen","given":"Jingwei","family":"Chen","affiliation":"University of Denver Denver , CO , USA"},{"name":"Robert C. Holte","slug":"robert-c-holte","given":"Robert C.","family":"Holte","affiliation":"University of Alberta Edmonton , AB , Canada"},{"name":"Sandra Zilles","slug":"sandra-zilles","given":"Sandra","family":"Zilles","affiliation":"University of Regina Regina , SK , Canada"},{"name":"Nathan R. Sturtevant","slug":"nathan-r-sturtevant","given":"Nathan R.","family":"Sturtevant","affiliation":"University of Denver Denver , CO , USA"}],"abstract":"It is well-known that any admissible unidirectional heuristic search algorithm must expand all states whose f-value is smaller than the optimal solution cost when using a consistent heuristic. Such states are called “surely expanded” (s.e.). A recent study characterized s.e. pairs of states for bidirectional search with consistent heuristics: if a pair of states is s.e. then at least one of the two states must be expanded. This paper derives a lower bound, VC, on the minimum number of expansions required to cover all s.e. pairs, and present a new admissible front-to-end bidirectional heuristic search algorithm, Near-Optimal Bidirectional Search (NBS), that is guaranteed to do no more than 2VC expansions. We further prove that no admissible front-to-end algorithm has a worst case better than 2VC. Experimental results show that NBS competes with or outperforms existing bidirectional search algorithms, and often outperforms A* as well.","doi":"10.24963/ijcai.2017/69","url":"https://ijcai.org/proceedings/2017/69","pdf":"https://ijcai.org/proceedings/2017/0069.pdf","markdown":"https://ijcai.org/proceedings/2017/69.md","bibtex":"https://ijcai.org/proceedings/2017/bibtex/69","volume":{"slug":"2017","title":"Proceedings of the Twenty-Sixth International Joint Conference on Artificial Intelligence","short_title":"IJCAI 2017","url":"https://ijcai.org/proceedings/2017/","year":2017,"location":"Melbourne, Australia","dates":"19-25 August 2017","editors":"Carles Sierra","isbn":"978-0-9992411-0-3","publisher":"International Joint Conferences on Artificial Intelligence Organization","doi_prefix":"10.24963/ijcai.2017"},"section":"Combinatorial & Heuristic Search","track":"Main track","number":69,"pages":{"first":489,"last":495},"keywords":["Combinatorial & Heuristic Search: Heuristic Search","Combinatorial & Heuristic Search: Combinatorial search/optimisation"],"videos":[],"references":[{"position":1,"raw":"[Barker and Korf, 2015] Joseph Kelly Barker and Richard E. 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