Source code for whalrus.rules.rule_schulze

# -*- coding: utf-8 -*-
"""
Copyright Sylvain Bouveret, Yann Chevaleyre and Fran├žois 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