CPO-STV: Difference between revisions
CPO-STV can be made faster to compute and modified to be Droop-proportional.
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(CPO-STV can be made faster to compute and modified to be Droop-proportional.) |
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At this point, we know that {A, C} is the Condorcet winner. Therefore, CPO-STV elects Andrea and Carter.
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=== Notes ===
CPO-STV can be highly computationally complex when there are many candidates, as if there are, say, 5 seats to be filled and 60 candidates, then there are 60 choose 5 = 5,461,512 possible outcomes.
It has not been proven whether CPO-STV is proportional for Droop solid coalitions.
One suggestion to modify CPO-STV to be guaranteeably proportional for Droop solid coalitions is to first eliminate all outcomes from consideration that fail Droop proportionality. In the above example, if there are 4 solid coalitions of 5 candidates each, then the upper bound of outcomes to consider is ((5^4) * 60) = 37500 outcomes, which is a reduction of outcomes to consider by a factor of about 145.
Several other such modifications are possible to reduce the number of outcomes to consider, some of which can potentially elect some outcome other than what CPO-STV would. Some are:
- As a first guess, calculate the STV outcome and see if it can win against all other outcomes (that are in consideration).
- If a set of candidates X is ranked above or equal to a set of candidates Y on all ballots, ignore all outcomes featuring candidates from Y but not X.
== See also ==
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