# -*- coding: utf-8 -*-
"""
Copyright Sylvain Bouveret, Yann Chevaleyre and François Durand
sylvain.bouveret@imag.fr, yann.chevaleyre@dauphine.fr, fradurand@gmail.com
This file is part of Whalrus.
Whalrus is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
Whalrus is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with Whalrus. If not, see <http://www.gnu.org/licenses/>.
"""
from whalrus.rules.rule import Rule
from whalrus.rules.rule_iterated_elimination import RuleIteratedElimination
from whalrus.rules.rule_plurality import RulePlurality
from whalrus.eliminations.elimination import Elimination
from whalrus.eliminations.elimination_last import EliminationLast
from whalrus.priorities.priority import Priority
[docs]class RuleIRV(RuleIteratedElimination):
"""
Instant-Runoff Voting, also known as Alternative Vote, Single Transferable Vote, etc.
Parameters
----------
args
Cf. parent class.
base_rule : Rule
Default: :class:`RulePlurality`.
elimination : Elimination
Default: :class:`EliminationLast` with ``k=1``.
kwargs
Cf. parent class.
Examples
--------
At each round, the candidate with the worst Plurality score is eliminated.
>>> rule = RuleIRV(['a > b > c', 'b > a > c', 'c > a > b'], weights=[2, 3, 4])
>>> rule.eliminations_[0].rule_.gross_scores_
{'a': 2, 'b': 3, 'c': 4}
>>> rule.eliminations_[1].rule_.gross_scores_
{'b': 5, 'c': 4}
>>> rule.eliminations_[2].rule_.gross_scores_
{'b': 9}
>>> rule.winner_
'b'
An example using the tie-break:
>>> rule = RuleIRV(['a > c > b', 'b > a > c', 'c > a > b'], weights=[1, 2, 1],
... tie_break=Priority.ASCENDING)
>>> rule.eliminations_[0].rule_.gross_scores_
{'a': 1, 'b': 2, 'c': 1}
>>> rule.eliminations_[1].rule_.gross_scores_
{'a': 2, 'b': 2}
>>> rule.eliminations_[2].rule_.gross_scores_
{'a': 4}
>>> rule.winner_
'a'
"""
def __init__(self, *args, base_rule: Rule = None, elimination: Elimination = None, **kwargs):
if base_rule is None:
base_rule = RulePlurality()
if elimination is None:
elimination = EliminationLast(k=1)
super().__init__(*args, base_rule=base_rule, elimination=elimination, **kwargs)