{"type":"ScholarlyArticle","title":"Improved Approximation Ratio for Strategyproof Facility Location on a Cycle","authors":[{"name":"Krzysztof Rogowski","slug":"krzysztof-rogowski","given":"Krzysztof","family":"Rogowski","affiliation":""},{"name":"Marcin Dziubiński","slug":"marcin-dziubinski","given":"Marcin","family":"Dziubiński","affiliation":""}],"abstract":"We study the problem of design of strategy-proof in expectation (SP) mechanisms for facility location on a cycle, with the objective of minimizing the sum of costs of n agents. We show that there exists an SP mechanism that attains an approximation ratio of 7/4 with respect to the sum of costs of the agents, thus improving the best known upper bound of 2 - 2/n in the cases of n ≥ 5. The mechanism obtaining the bound randomizes between two mechanisms known in the literature: the Random Dictator (RD) and the Proportional Circle Distance (PCD) mechanism of Meir (2019). To prove the result, we propose a cycle-cutting technique that allows for estimating the problem on a cycle by a problem on a line.","doi":"10.24963/ijcai.2025/449","url":"https://ijcai.org/proceedings/2025/449","pdf":"https://ijcai.org/proceedings/2025/0449.pdf","markdown":"https://ijcai.org/proceedings/2025/449.md","bibtex":"https://ijcai.org/proceedings/2025/bibtex/449","volume":{"slug":"2025","title":"Proceedings of the Thirty-Fourth International Joint Conference on Artificial Intelligence","short_title":"IJCAI 2025","url":"https://ijcai.org/proceedings/2025/","year":2025,"location":"Montreal, Canada","dates":"16-22 August 2025","editors":"James Kwok","isbn":"978-1-956792-06-5","publisher":"International Joint Conferences on Artificial Intelligence Organization","doi_prefix":"10.24963/ijcai.2025"},"section":"Game Theory and Economic Paradigms","track":"Main Track","number":449,"pages":{"first":4032,"last":4039},"keywords":["Game Theory and Economic Paradigms: GTEP: Mechanism design","Multidisciplinary Topics and Applications: MTA: Economics","Game Theory and Economic Paradigms: GTEP: Auctions and market-based systems","Game Theory and Economic Paradigms: GTEP: Noncooperative games"],"videos":[],"references":[],"license_note":"Copyright International Joint Conferences on Artificial Intelligence."}