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Improved Heuristic for Manipulation of Second-order Copeland Elections

13 pagesPublished: October 19, 2017


The \textit{second-order Copeland} voting scheme is NP-complete to manipulate even if a manipulator has perfect information about the preferences of other voters in an election.~A recent work proposes a \textit{branch-and-bound} heuristic for manipulation of second-order Copeland elections.~The work shows that there are instances of the elections that may be manipulated using the branch-and-bound heuristic.~However, the performance of the heuristic degraded for fairly large number of candidates in elections.~We show that this heuristic is \textit{exponential} in the number of candidates in an election, and propose an improved heuristic that extends this previous work.~Our improved heuristic is based on \textit{randomization technique} and is shown to be \textit{polynomial} in the number of candidates in an election.~We also account for the number of samples required for a given accuracy and the probability of missing the accurate value of the number of manipulations in an election.

Keyphrases: Branch and Bound, Copeland Election, randomised heuristic

In: Christoph Benzmüller, Christine Lisetti and Martin Theobald (editors). GCAI 2017. 3rd Global Conference on Artificial Intelligence, vol 50, pages 162--174

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