[EM] CIVS update

Andrew Myers andru at cs.cornell.edu
Sat Nov 6 08:46:21 PST 2004

On Fri, Nov 05, 2004 at 06:05:05PM -0800, Dr.Ernie Prabhakar wrote:
> On Nov 1, 2004, at 1:27 PM, Andrew Myers wrote:
> >I thought people might be interested to know about some
> >recent improvements to the Condorcet Internet Voting Service at
> >http://www5.cs.cornell.edu/~andru/civs.
> >
> >* It now implements three different completion rules, including
> >  MAM, Beatpath Winner, and a deterministic variant of MAM.
> I presume this"deterministic variant " is what you call CIVS Ranked 
> Pairs:
> http://www5.cs.cornell.edu/~andru/civs/rp.html
> >The major difference between CIVS Ranked Pairs and MAM is the rule on 
> >when to keep a preference. A preference is kept exactly when it does 
> >not create any new cycles when considered in conjunction with strictly 
> >stronger, kept preferences. Thus, preferences of equal strength may be 
> >kept even though in conjunction they produce a new cycle, as long as 
> >individually they do not.
> This sounds to me that Same-Sized Majorities with no other 
> differentiators will lead to cycles, and CIVS specifies no mechanism 
> for breaking that, and is thus incomplete.  Is that correct?
> -- Ernie P.

That is correct, and intentional.  CIVS RP doesn't have either of the two
random tie-breaking mechanisms in MAM, which are necessary to ensure
that you always obtain a total ordering of the alternatives.

-- Andrew

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