http://bolson.org/voting/sim_one_seat/20090810/
I think a few of these plots show Single Transferrable Vote behaving badly in the same ways IRV does, with discontinuities and irregular solution spaces.
I also ran Condorcet and IRNR using combinatoric expansion. Combinatoric variants of single winner election methods adapt to multiwinner situations by enumerating all possible winning sets of the available choices and using a simulated voter's preferences on the choices in each set to determine a preference for each winner-set. Voting on the n-choose-k preferences for winner-sets then procedes as for a single-winner election.
I think based on this I'm going to have to think more about making native multiwinner methods. Combinatoric expansion gets pretty expensive for large numbers of choices or seats to elect. I had been kinda resigned to STV being the state of the art in multiwinner methods, but we seriously ought to be able to do better.
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