# -*- 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_score_num_row_sum import RuleScoreNumRowSum
from whalrus.converters_ballot.converter_ballot_to_order import ConverterBallotToOrder
from whalrus.utils.utils import cached_property
from whalrus.converters_ballot.converter_ballot import ConverterBallot
from whalrus.matrices.matrix import Matrix
from whalrus.matrices.matrix_majority import MatrixMajority
[docs]class RuleCopeland(RuleScoreNumRowSum):
"""
Copeland's rule.
Parameters
----------
args
Cf. parent class.
converter : ConverterBallot
Default: :class:`ConverterBallotToOrder`.
matrix : Matrix
Default: :class:`MatrixMajority`.
kwargs
Cf. parent class.
Examples
--------
The score of a candidate is the number of victories in the majority matrix.
>>> rule = RuleCopeland(ballots=['a > b > c', 'b > a > c', 'c > a > b'])
>>> rule.matrix_.as_array_
array([[Fraction(1, 2), 1, 1],
[0, Fraction(1, 2), 1],
[0, 0, Fraction(1, 2)]], dtype=object)
>>> rule.scores_
{'a': 2, 'b': 1, 'c': 0}
"""
def __init__(self, *args, converter: ConverterBallot = None, matrix: Matrix = None, **kwargs):
if converter is None:
converter = ConverterBallotToOrder()
if matrix is None:
matrix = MatrixMajority()
super().__init__(*args, converter=converter, matrix=matrix, **kwargs)
@cached_property
def matrix_majority_(self):
"""Matrix: The majority matrix. This is an alias for :attr:`matrix_`.
Examples
--------
>>> rule = RuleCopeland(ballots=['a > b > c', 'b > a > c', 'c > a > b'])
>>> rule.matrix_majority_.as_array_
array([[Fraction(1, 2), 1, 1],
[0, Fraction(1, 2), 1],
[0, 0, Fraction(1, 2)]], dtype=object)
"""
return self.matrix_