Possible winners when new alternatives join: new results coming up!
AAMAS(2011)
摘要
In a voting system, sometimes multiple new alternatives will join the election after the voters' preferences over the initial alternatives have been revealed. Computing whether a given alternative can be a co-winner when multiple new alternatives join the election is called the possible co-winner with new alternatives (PcWNA) problem and was introduced by Chevaleyre et al. 6]. In this paper, we show that the PcWNA problems are NP-complete for the Bucklin, Copeland0, and maximin (a.k.a. Simpson) rule, even when the number of new alternatives is no more than a constant. We also show that the PcWNA problem can be solved in polynomial time for plurality with runoff. For the approval rule, we examine three different ways to extend a linear order with new alternatives, and characterize the computational complexity of the PcWNA problem for each of them.
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关键词
different way,approval rule,possible winner,new result,polynomial time,initial alternative,new alternative,linear order,pcwna problem,computational complexity,possible co-winner,multiple new alternative
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