Schulze and Ranked-Pairs Voting are Fixed-Parameter Tractable to Bribe,   Manipulate, and Control
  Schulze and ranked-pairs elections have received much attention recently, and the former has quickly become a quite widely used election system. For many cases these systems have been proven resistant to bribery, control, or manipulation, with ranked pairs being particularly praised for being NP-hard for all three of those. Nonetheless, the present paper shows that with respect to the number of candidates, Schulze and ranked-pairs elections are fixed-parameter tractable to bribe, control, and manipulate: we obtain uniform, polynomial-time algorithms whose degree does not depend on the number of candidates. We also provide such algorithms for some weighted variants of these problems. 
Lane A. Hemaspaandra, Rahman Lavaee, Curtis Menton
cs.GT cs.DS cs.MA