Manipulation of copeland elections

We resolve an open problem regarding the complexity of unweighted coalitional manipulation, namely, the complexity of Copeland -manipulation for {0, 1}. Copeland , 0 1, is an election system where for each pair of candidates we check which one is preferred by more voters (i.e., we conduct a head-to-head majority contest) and we give one point to this candidate and zero to the other. However, in case of a tie both candidates receive points. In the end, candidates with most points win. It is known [13] that Copeland -manipulation is NP-complete for all rational 's in (0, 1) - {0.5} (i.e., for all the reasonable cases except the three truly interesting ones). In this paper we show that the problem remains NP-complete for {0, 1}. In addition, we resolve the complexity of Copeland -manipulation for each rational [0, 1] for the case of irrational voters. Categories and Subject Descriptors I.2.11 [Artificial Intelligence]: Distributed Artificial Intelligence--Multiagent System...

• Type: Conference
• Year: 2010
• Where: ATAL
• Authors: Piotr Faliszewski, Edith Hemaspaandra, Henning Schnoor
• Keywords: ATAL 2010, Candidates Receive Points, Copeland -manipulation, Intelligent Agents, Unweighted Coalitional Manipulation