Multivariate Complexity Analysis of Swap Bribery

  • Authors:
  • Britta Dorn;Ildikó Schlotter

  • Affiliations:
  • Universität Ulm, Fakultät für Mathematik und Wirtschaftswissenschaften, Helmholtzstr. 18, 89081, Ulm, Germany;Budapest University of Technology and Economics, Department of Computer Science and Information Theory, Magyar tudósok körútja 2, 1117, Budapest, Hungary

  • Venue:
  • Algorithmica - Special Issue: Parameterized and Exact Computation, Part I
  • Year:
  • 2012

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Abstract

We consider the computational complexity of a problem modeling bribery in the context of voting systems. In the scenario of Swap Bribery, each voter assigns a certain price for swapping the positions of two consecutive candidates in his preference ranking. The question is whether it is possible, without exceeding a given budget, to bribe the voters in a way that the preferred candidate wins in the election. We initiate a parameterized and multivariate complexity analysis of Swap Bribery, focusing on the case of k-approval. We investigate how different cost functions affect the computational complexity of the problem. We identify a special case of k-approval for which the problem can be solved in polynomial time, whereas we prove NP-hardness for a slightly more general scenario. We obtain fixed-parameter tractability as well as W[1]-hardness results for certain natural parameters.