论文标题

在木琴模型下找到第二好的候选人

Finding the Second-Best Candidate under the Mallows Model

论文作者

Liu, Xujun, Milenkovic, Olgica

论文摘要

在顺序分析和最佳停止理论中,著名的秘书问题要求一个人最大化在依次检查的列表中找到最佳候选人的概率,即接受/拒绝决策是实时做出的。该问题的一个版本是所谓的博士后问题,为此,感兴趣的问题是设计一种策略,该策略确定了第二好的候选人,并具有最高的成功概率。 我们以组合形式研究了博士后问题。在这种情况下,根据对称组$ s_n $的某些分布来对置换$ n $的排列$π$进行采样,并且$π$的元素从左到右均一揭示,以便在每个步骤中只能观察到元素的相对顺序。在每个步骤中,都必须决定接受或拒绝当前提出的要素,并且将来不能回忆起决定。感兴趣的问题是找到选择第二大价值的位置的最佳策略。我们解决了未经传统设置的DOSDOC问题,在该设置中,候选者并非随机均匀地呈现,而是根据曲棍球分布提取的排列。 Mallows Distribution分配给每个排列$π\ s_n $ A权重$θ^{c(π)} $,其中函数C计数$π$中的反转数。为了确定明显更具挑战性的博士后问题的最佳停止标准,我们采用了一种组合方法,其中包括新的证明技术和新型方法论扩展,与秘书问题设置中首次介绍的分析相比。最佳策略取决于Mallows分布的参数$θ$,并且可以通过求解明确定义的复发关系来确定。

The well-known secretary problem in sequential analysis and optimal stopping theory asks one to maximize the probability of finding the optimal candidate in a sequentially examined list under the constraint that accept/reject decisions are made in real-time. A version of the problem is the so-called postdoc problem, for which the question of interest is to devise a strategy that identifies the second-best candidate with highest possible probability of success. We study the postdoc problem in its combinatorial form. In this setting, a permutation $π$ of length $N$ is sampled according to some distribution on the symmetric group $S_N$ and the elements of $π$ are revealed one-by-one from left to right so that at each step, one can only observe the relative orders of the elements. At each step, one must decide to either accept or reject the currently presented element and cannot recall the decision in the future. The question of interest is to find the optimal strategy for selecting the position of the second-largest value. We solve the postdoc problem for the untraditional setting where the candidates are not presented uniformly at random but rather according to permutations drawn from the Mallows distribution. The Mallows distribution assigns to each permutation $π\in S_N$ a weight $θ^{c(π)}$, where the function c counts the number of inversions in $π$. To identify the optimal stopping criteria for the significantly more challenging postdoc problem, we adopt a combinatorial methodology that includes new proof techniques and novel methodological extensions compared to the analysis first introduced in the setting of the secretary problem. The optimal strategies depend on the parameter $θ$ of the Mallows distribution and can be determined exactly by solving well-defined recurrence relations.

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