{"type":"ScholarlyArticle","title":"When Votes Change and Committees Should (Not)","authors":[{"name":"Robert Bredereck","slug":"robert-bredereck","given":"Robert","family":"Bredereck","affiliation":"Institut für Informatik , TU Clausthal , Germany; Humboldt-Universität zu Berlin , Berlin , Germany"},{"name":"Till Fluschnik","slug":"till-fluschnik","given":"Till","family":"Fluschnik","affiliation":"Technische Universität Berlin , Faculty IV, Algorithmics and Computational Complexity , Germany"},{"name":"Andrzej Kaczmarczyk","slug":"andrzej-kaczmarczyk","given":"Andrzej","family":"Kaczmarczyk","affiliation":"Technische Universität Berlin , Faculty IV, Algorithmics and Computational Complexity , Germany; AGH University , Kraków , Poland"}],"abstract":"Electing a single committee of a small size is a classical and well-understood voting situation. Being interested in a sequence of committees, we introduce two time-dependent multistage models based on simple scoring-based voting. Therein, we are given a sequence of voting profiles (stages) over the same set of agents and candidates, and our task is to find a small committee for each stage of high score. In the conservative model we additionally require that any two consecutive committees have a small symmetric difference. Analogously, in the revolutionary model we require large symmetric differences. We prove both models to be NP-hard even for a constant number of agents, and, based on this, initiate a parameterized complexity analysis for the most natural parameters and combinations thereof. Among other results, we prove both models to be in XP yet W[1]-hard regarding the number of stages, and that being revolutionary seems to be \"easier\" than being conservative.","doi":"10.24963/ijcai.2022/21","url":"https://ijcai.org/proceedings/2022/21","pdf":"https://ijcai.org/proceedings/2022/0021.pdf","markdown":"https://ijcai.org/proceedings/2022/21.md","bibtex":"https://ijcai.org/proceedings/2022/bibtex/21","volume":{"slug":"2022","title":"Proceedings of the Thirty-First International Joint Conference on Artificial Intelligence","short_title":"IJCAI 2022","url":"https://ijcai.org/proceedings/2022/","year":2022,"location":"Vienna","dates":"23-29 July 2022","editors":"Luc De Raedt","isbn":"978-1-956792-00-3","publisher":"International Joint Conferences on Artificial Intelligence Organization","doi_prefix":"10.24963/ijcai.2022"},"section":"Agent-based and Multi-agent Systems","track":"Main Track","number":21,"pages":{"first":144,"last":150},"keywords":["Agent-based and Multi-agent Systems: Computational Social Choice"],"videos":[{"label":"Video #1","url":"https://slideslive.com/38986766","length_sec":92,"provider":"slideslive"},{"label":"Video #2","url":"https://slideslive.com/38984909","length_sec":361,"provider":"slideslive"}],"references":[{"position":1,"raw":"[Aziz and Lee, 2018] H. 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