Class: Equalshares::Rules::CardinalMes

Inherits:
Base
  • Object
show all
Defined in:
lib/equalshares/rules/cardinal_mes.rb

Overview

Method of Equal Shares for ballots carrying per-voter utilities (vote_type "scoring"/"cumulative", or "ordinal" via Borda), where each voter i has a per-project utility u_i(c). Faithful port of the core of pabutools' method_of_equal_shares with an additive satisfaction (the "poor/rich" affordability computation), for the pure rule (no completion).

The approval path (Rules::MethodOfEqualShares) is kept separate; this general path is used when instance.cardinal? is true.

Instance Method Summary collapse

Methods inherited from Base

call, #initialize

Constructor Details

This class inherits a constructor from Equalshares::Rules::Base

Instance Method Details

#call ⇒ Object 



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# File 'lib/equalshares/rules/cardinal_mes.rb', line 14

def call
  unless instance.cardinal?
    raise ComputeError,
          "CardinalMes applies to instances with per-voter scores (scoring/cumulative/ordinal)"
  end

  start = now
  voter_ids = election.voter_ids
  project_ids = election.project_ids
  approvers = election.approvers
  cost = election.costs
  budget_limit = election.budget
  util = project_ids.to_h { |c| [c, election.utilities(c)] }
  n = voter_ids.length

  budget = {}
  voter_ids.each { |i| budget[i] = budget_limit / n } # endowment B/|N|

  remaining = project_ids.select { |c| cost[c].positive? && !approvers[c].empty? }
  winners = []

  loop do
    argmin = argmin_by_affordability(remaining, approvers, budget, util, cost)
    break if argmin.empty?

    selected = Tie.resolve_one(project_ids, cost, approvers, params, argmin)
    charge(selected, approvers, budget, util, cost)
    winners << selected
    remaining.delete(selected)
    progress&.call((100 * winners.sum { |c| cost[c] } / budget_limit).floor)
  end

  result(winners, start)
end