Schulze and ranked-pairs voting are fixed-parameter tractable to bribe, manipulate, and control
Lane A. Hemaspaandra, Rahman Lavaee, Curtis Menton · arXiv (Cornell University) · 2013
Schulze and ranked-pairs elections have received attention recently, with the former having quickly become a widely used election system. For many cases these systems have been proven resistant to bribery, control, and manipulation, with ranked pairs being particularly praised for being NP-hard for all three of those. Nonetheless, this work shows that with respect to the number of candidates, both Schulze and ranked-pairs elections are fixed-parameter tractable to bribe, control, and manipulate: we can obtain uniform, polynomial-time algorithms whose degree does not depend on the number of candidates.