# -*- 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.converters_ballot.converter_ballot_to_order import ConverterBallotToOrder
from whalrus.utils.utils import cached_property, NiceSet
from whalrus.converters_ballot.converter_ballot import ConverterBallot
from whalrus.matrices.matrix import Matrix
from whalrus.matrices.matrix_schulze import MatrixSchulze
[docs]class RuleSchulze(Rule):
"""
Schulze's Rule.
A candidate is a Schulze winner if it has no defeat in the Schulze matrix.
Parameters
----------
args
Cf. parent class.
converter : ConverterBallot
Default: :class:`ConverterBallotToOrder`.
matrix_schulze : Matrix
The Schulze matrix. Default: :class:`MatrixSchulze`.
kwargs
Cf. parent class.
Examples
--------
>>> rule = RuleSchulze(['a > b > c', 'b > c > a', 'c > a > b'], weights=[4, 3, 2])
>>> rule.matrix_schulze_.as_array_
array([[0, Fraction(2, 3), Fraction(2, 3)],
[Fraction(5, 9), 0, Fraction(7, 9)],
[Fraction(5, 9), Fraction(5, 9), 0]], dtype=object)
>>> rule.winner_
'a'
"""
def __init__(self, *args, converter: ConverterBallot = None, matrix_schulze: Matrix = None, **kwargs):
if converter is None:
converter = ConverterBallotToOrder()
if matrix_schulze is None:
matrix_schulze = MatrixSchulze()
self.matrix_schulze = matrix_schulze
super().__init__(*args, converter=converter, **kwargs)
@cached_property
def matrix_schulze_(self):
"""Matrix: The Schulze matrix (once computed with the given profile).
"""
return self.matrix_schulze(self.profile_converted_)
@cached_property
def order_(self) -> list:
m = self.matrix_schulze_
victories = {(c, d) for (c, d) in m.as_dict_.keys() if m.as_dict_[(c, d)] > m.as_dict_[(d, c)]}
to_sort = self.candidates_.copy()
result = []
while to_sort:
losers = {d for (c, d) in victories}
result.append(to_sort - losers)
to_sort = losers
victories = {(c, d) for (c, d) in victories if c in to_sort and d in to_sort}
return result