论文标题
大选有多大的可能性?
How Likely Are Large Elections Tied?
论文作者
论文摘要
在许多学科中,了解选举的可能性是一个古典话题,包括社会选择,游戏理论,政治学和公共选择。尽管有很多文学和普遍的信念是罕见的关系,但对大选中的罕见关系知之甚少,除了在I.I.D.下进行一些简单的位置评分规则。统一的投票分布,被称为社会选择中的公正文化(IC)。特别是,在Marchant明确提出IC下的K-Way关系的可能性之后,几乎没有取得进展。 我们为公开问题提供了一个渐近答案,该问题是一个比I.I.D的模型更笼统和现实的广泛研究的投票规则。模型(尤其是IC) - Xia平滑的社会选择框架,其灵感来自Spielman和Teng的著名复杂性分析。我们证明了关于位置评分规则,基于边缘订单的规则和一些基于多场得分的消除规则的关系的平滑可能性的二分法定理,其中包括常见研究的投票规则,例如多数,Borda,Borda,eveto,否决,否决权,Copeland,Copeland,Copeland,Schulze,Schulze,Schulze,Schulze,STV和Coombs As Persece assepers。我们还通过对Preflib上的合成数据和现实世界等级数据进行实验来补充理论结果。我们的主要技术工具是在多面体中用于泊松多官方变量的平滑可能性上的改进的二分法表征,这是通过探索V-代理与Polyhedra的矩阵表示之间的相互作用来证明的,并且可能具有独立的关注。
Understanding the likelihood for an election to be tied is a classical topic in many disciplines including social choice, game theory, political science, and public choice. Despite a large body of literature and the common belief that ties are rare, little is known about how rare ties are in large elections except for a few simple positional scoring rules under the i.i.d. uniform distribution over the votes, known as the Impartial Culture (IC) in social choice. In particular, little progress was made after Marchant explicitly posed the likelihood of k-way ties under IC as an open question in 2001. We give an asymptotic answer to the open question for a wide range of commonly studied voting rules under a model that is much more general and realistic than i.i.d. models (especially IC) -- the smoothed social choice framework by Xia that was inspired by the celebrated smoothed complexity analysis by Spielman and Teng. We prove dichotomy theorems on the smoothed likelihood of ties under positional scoring rules, edge-order-based rules, and some multi-round score-based elimination rules, which include commonly studied voting rules such as plurality, Borda, veto, maximin, Copeland, ranked pairs, Schulze, STV, and Coombs as special cases. We also complement the theoretical results by experiments on synthetic data and real-world rank data on Preflib. Our main technical tool is an improved dichotomous characterization on the smoothed likelihood for a Poisson multinomial variable to be in a polyhedron, which is proved by exploring the interplay between the V-representation and the matrix representation of polyhedra and might be of independent interest.