Multi-Winner Voting Games in TU and NTU: When is the Core Always Non-Empty?
多赢家投票游戏在完全信息和不完全信息下的核心是否总是非空?
Jiehua Chen, Christian Hatschka
AI总结 本文研究了多赢家投票游戏中,核心是否总是非空的问题,探讨了在不同投票规则下,转移效用和非转移效用模型下的核心存在性和计算方法。
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多赢家批准投票选择一个大小为k的委员会,以汇总选民对替代方案的批准偏好。一个核心问题是在联合稳定性:任何联盟不应能够选择一个委员会--大小不超过其比例份额--使得每个联盟成员都有严格更多的批准替代方案。这一概念由Aziz等人(2017)引入为核心稳定委员会,可以自然解释为一个非转移效用的核心概念。我们引入了多赢家投票游戏,一种合作博弈框架,它统一了先前的工作,并支持在不同投票规则下系统研究两种效用转移模型。玩家是选民。每个联盟有一个比例席位上限,并且只能提出不超过该大小的可行委员会。固定一个多赢家规则,每个可行委员会为联盟成员诱导一个效用向量。在可转移效用(TU)模型中,联盟可以重新分配可行委员会的总效用给其成员。在不可转移效用(NTU)模型中,联盟只能使用由某些可行委员会直接实现的效用向量。核心由可行的联盟效用向量组成,这些向量不被任何联盟阻止。一个联盟是阻止的,如果它能提出一个可行的委员会,使所有成员严格更高兴,直接在NTU中,或者在TU中经过重新分配后。当使用标准PAV/批准效用时,NTU核心等同于先前研究中研究的核心稳定委员会概念。据我们所知,多赢家投票的TU核心之前尚未被研究。我们分析了四种著名的规则:批准投票(AV)、满足批准投票(SAV)、切赫-库恩(CC)、比例批准投票(PAV)的核心存在性和计算方法。
Multi-winner approval voting selects a size-$k$ committee that aggregates voters' approval preferences over a set of alternatives. A central question is coalitional stability: No coalition should be able to pick a committee -- of size at most its proportional share -- under which every coalition member has strictly more approved alternatives. This notion, introduced by Aziz et al. (2017) as core-stable committees, is naturally interpreted as a core notion with non-transferable utility. We introduce multi-winner voting games, a cooperative-game framework that unifies prior work and supports a systematic study of two utility-transfer models across different voting rules. Players are voters. Each coalition has a proportional seat cap and may only propose admissible committees up to that size. Fixing a multi-winner rule, each admissible committee induces a utility vector for the members of the coalition. In the transferable utility (TU) model, a coalition may redistribute the total utility of an admissible committee among its members. In the non-transferable utility (NTU) model, a coalition may only use utility vectors that are realized directly by some admissible committee. The core consists of utility vectors feasible for the grand coalition that are not blocked by any coalition. A coalition is blocking if it can propose an admissible committee that makes all its members strictly better off, directly in NTU and after redistribution in TU. When instantiated with the standard PAV/approval utility, the NTU-core is equivalent to the core-stable committee concept studied in prior work. To our knowledge, the TU-core for multi-winner voting has not been previously studied. We analyze core existence and computation for four prominent rules: Approval Voting (AV), Satisfaction Approval Voting (SAV), Chamberlin--Courant (CC), Proportional Approval Voting (PAV).