[EM] Condorcet divisor method proportional representation

[Kristofer Munsterhjelm]

Ross Hyman wrote:
> A Condorcet divisor method proportional representation procedure is 
> presented that is a variant of Nicolaus Tideman’s Comparison of Pairs of 
> Outcomes by Single Transferable Vote (CPO-STV) and Shultz STV but 
> requires the determination of fewer candidate set comparisons than 
> either.  The method will produce the same result as a party list 
> election that uses the same divisor method provided that each voter 
> votes their party’s list.  The procedure is a Condorcet variant of the 
> procedure presented in the February 2011 issue of Voting Matters.

That's interesting. The way you make an ordering based on limited 
information reminds me of Ranked Pairs: you lock each relation and then 
skip those that would contradict what's already locked.

I imagine it would be possible to make a Schulze STV variant of the 
above, too: just calculate the relations as you've done, then use a 
strongest path algorithm to extrapolate the other pairwise contests. 
Schulze STV itself does this because it only directly knows the pairwise 
contests where the sets compared differ by a single candidate.

Apart from that, I also find the divisor approach of interest, because I 
have tried to make a multiwinner method based on divisor party list PR 
methods before. I found a method that was monotone and did reduce to 
party list PR if everybody voted for their parties' lists, but it was 
rather unwieldy. I wonder if your method is monotone -- do you know 
whether it is?