def tau_sincere(self):
"""Tau-vector associated to sincere voting.
Returns
-------
TauVector
* In Approval, all voters approve of their top candidate, and voters approve of their middle candidate if
and only if their utility for her is strictly greater than 0.5.
* In Plurality, all voters vote for their top candidate.
* In Anti-plurality, all voters vote against their bottom candidate (i.e. for the other two).
Notes
-----
In Plurality and Anti-plurality, sincere and fanatic voting are the same. They differ only in Approval.
"""
t = self.d_ballot_share_weak_voters_sincere.copy()
for ranking in RANKINGS:
if self.voting_rule == APPROVAL:
share_vote_one_two = self.have_ranking_with_utility_above_u(ranking, Fraction(1, 2))
share_vote_one = self.d_ranking_share[ranking] - share_vote_one_two
t[ballot_one(ranking)] += share_vote_one
t[ballot_one_two(ranking)] += share_vote_one_two
elif self.voting_rule == PLURALITY:
t[ballot_one(ranking)] += self.d_ranking_share[ranking]
elif self.voting_rule == ANTI_PLURALITY:
t[ballot_one_two(ranking)] += self.d_ranking_share[ranking]
else:
raise NotImplementedError
return TauVector(t, voting_rule=self.voting_rule, symbolic=self.symbolic)
def is_equilibrium(self, strategy):
"""Whether a strategy is an equilibrium.
Parameters
----------
strategy : StrategyTwelve
A strategy that specifies at least all the rankings that are present in the profile.
Returns
-------
EquilibriumStatus
Whether `strategy` is an equilibrium in this profile.
Examples
--------
>>> from fractions import Fraction
>>> profile = ProfileTwelve({'ab_c': Fraction(1, 10), 'b_ac': Fraction(6, 10),
... 'c_ab': Fraction(2, 10), 'ca_b': Fraction(1, 10)})
>>> strategy = StrategyTwelve({'abc': 'ab', 'bac': 'b', 'cab': 'utility-dependent'})
>>> profile.is_equilibrium(strategy)
EquilibriumStatus.EQUILIBRIUM
"""
d_ranking_best_response = self.tau(strategy).d_ranking_best_response
status = EquilibriumStatus.EQUILIBRIUM
for ranking, share in self.d_ranking_share.items():
if share == 0:
continue
best_response = d_ranking_best_response[ranking]
if best_response.ballot == INCONCLUSIVE: # pragma: no cover - Should never happen
status = min(status, EquilibriumStatus.INCONCLUSIVE)
else:
type_1 = ranking[:1] + '_' + ranking[1:] # E.g. a_bc
type_12 = ranking[:2] + '_' + ranking[2:] # E.g. ab_c
if best_response.ballot == UTILITY_DEPENDENT:
if self.voting_rule == APPROVAL:
best_ballot_1, best_ballot_12 = ballot_one(
ranking), ballot_one_two(ranking)
elif self.voting_rule == PLURALITY:
best_ballot_1, best_ballot_12 = ballot_one(
ranking), ballot_two(ranking)
elif self.voting_rule == ANTI_PLURALITY:
best_ballot_1, best_ballot_12 = ballot_one_three(
ranking), ballot_one_two(ranking)
else:
raise NotImplementedError
else:
best_ballot_1 = best_response.ballot
best_ballot_12 = best_response.ballot
if self.d_type_share[type_1] > 0 and getattr(
strategy, type_1) != best_ballot_1:
return EquilibriumStatus.NOT_EQUILIBRIUM
if self.d_type_share[type_12] > 0 and getattr(
strategy, type_12) != best_ballot_12:
return EquilibriumStatus.NOT_EQUILIBRIUM
return status
def share_sincere_among_strategic_voters(self, strategy):
"""Share of strategic voters that happen to cast a sincere ballot.
Parameters
----------
strategy : StrategyTwelve
A strategy that specifies at least all the rankings that are present in the profile.
Returns
-------
Number
The ratio of sincere voters among strategic voters.
Examples
--------
>>> from fractions import Fraction
>>> profile = ProfileTwelve({'ab_c': Fraction(1, 10), 'b_ac': Fraction(6, 10),
... 'c_ab': Fraction(2, 10), 'ca_b': Fraction(1, 10)})
>>> strategy = StrategyTwelve({'abc': 'ab', 'bac': 'b', 'cab': 'utility-dependent'})
>>> profile.share_sincere_among_strategic_voters(strategy)
1
"""
assert self.voting_rule == strategy.voting_rule
# Weak orders: these voters are always "sincere", even in Plurality or Anti-Plurality. For example, in
# Plurality, a voter a~b>c will either vote for a or b, and this is considered "sincere".
share_sincere = sum(self.d_weak_order_share.values())
# Rankings
for ranking, ballot in strategy.d_ranking_ballot.items():
if self.d_ranking_share[ranking] == 0:
continue
# For a ranking abc, ballot can be real ballots (e.g. 'a', 'ab'), '' or 'utility-dependent'.
if self.voting_rule == APPROVAL:
if ballot == ballot_one(ranking):
share_sincere += self.have_ranking_with_utility_below_u(
ranking, u=.5)
elif ballot == ballot_one_two(ranking):
share_sincere += self.have_ranking_with_utility_above_u(
ranking, u=.5)
else:
share_sincere += self.d_ranking_share[ranking]
elif self.voting_rule == PLURALITY:
if ballot == ballot_one(ranking):
share_sincere += self.d_ranking_share[ranking]
elif ballot == UTILITY_DEPENDENT:
share_sincere += self.have_ranking_with_utility_below_u(
ranking, u=.5)
elif self.voting_rule == ANTI_PLURALITY:
if ballot == ballot_one_two(ranking):
share_sincere += self.d_ranking_share[ranking]
elif ballot == UTILITY_DEPENDENT:
share_sincere += self.have_ranking_with_utility_above_u(
ranking, u=.5)
else:
raise NotImplementedError
return self.ce.simplify(share_sincere)
def _f(self):
if getattr(self, ranking) == UTILITY_DEPENDENT:
if getattr(self, 'voting_rule') in {APPROVAL, ANTI_PLURALITY}:
return ballot_one_two(ranking)
elif getattr(self, 'voting_rule') == PLURALITY:
return ballot_two(ranking)
else:
raise NotImplementedError
return getattr(self, ranking)
def __init__(self,
d_ranking_ballot,
d_weak_order_ballot=None,
profile=None,
voting_rule=None):
"""
>>> strategy = StrategyOrdinal({'abc': 'non_existing_ballot'})
Traceback (most recent call last):
ValueError: Unknown strategy: non_existing_ballot
"""
voting_rule = self._get_voting_rule_(profile, voting_rule)
# Prepare the dictionary of thresholds
d_ranking_threshold = DictPrintingInOrderIgnoringZeros()
for ranking, ballot in d_ranking_ballot.items():
if ballot == '':
d_ranking_threshold[ranking] = None
elif ballot == ballot_one(ranking) and voting_rule in {
APPROVAL, PLURALITY
}:
d_ranking_threshold[ranking] = 1
elif ballot == ballot_two(ranking) and voting_rule == PLURALITY:
d_ranking_threshold[ranking] = 0
elif (ballot
in {ballot_one_two(ranking),
ballot_one_two(ranking)[::-1]}
and voting_rule in {APPROVAL, ANTI_PLURALITY}):
d_ranking_threshold[ranking] = 0
elif (ballot in {
ballot_one_three(ranking),
ballot_one_three(ranking)[::-1]
} and voting_rule == ANTI_PLURALITY):
d_ranking_threshold[ranking] = 1
else:
raise ValueError('Unknown strategy: ' + ballot)
# Call parent class
super().__init__(d=d_ranking_threshold,
d_weak_order_ballot=d_weak_order_ballot,
profile=profile,
voting_rule=voting_rule)
def __init__(self,
d,
d_weak_order_ballot=None,
ratio_optimistic=None,
profile=None,
voting_rule=None):
voting_rule = self._get_voting_rule_(profile, voting_rule)
# Prepare the dictionaries of thresholds and ratios
self.d_ranking_threshold = DictPrintingInOrderIgnoringNone(
{ranking: None
for ranking in RANKINGS})
self.d_ranking_ratio_optimistic = DictPrintingInOrderIgnoringNone(
{ranking: None
for ranking in RANKINGS})
for ranking, value in d.items():
if isinstance(value, tuple):
self.d_ranking_threshold[
ranking], self.d_ranking_ratio_optimistic[ranking] = value
else:
self.d_ranking_threshold[ranking] = value
self.d_ranking_ratio_optimistic[ranking] = ratio_optimistic
# Prepare the dictionary of ballots
d_ranking_ballot = DictPrintingInOrderIgnoringZeros()
for ranking, threshold in self.d_ranking_threshold.items():
if threshold is None:
d_ranking_ballot[ranking] = ''
elif threshold == 1:
if voting_rule in {APPROVAL, PLURALITY}:
d_ranking_ballot[ranking] = ballot_one(ranking)
elif voting_rule == ANTI_PLURALITY:
d_ranking_ballot[ranking] = ballot_one_three(ranking)
else:
raise NotImplementedError
elif threshold == 0:
if voting_rule in {APPROVAL, ANTI_PLURALITY}:
d_ranking_ballot[ranking] = ballot_one_two(ranking)
elif voting_rule == PLURALITY:
d_ranking_ballot[ranking] = ballot_two(ranking)
else:
raise NotImplementedError
else:
d_ranking_ballot[ranking] = UTILITY_DEPENDENT
# Call parent class
super().__init__(d_ranking_ballot=d_ranking_ballot,
d_weak_order_ballot=d_weak_order_ballot,
profile=profile,
voting_rule=voting_rule)
def tau_fanatic(self):
"""Tau-vector associated to fanatic voting.
Returns
-------
TauVector
In Approval or Plurality, all voters approve of their top candidate only. In Anti-Plurality, they all
disapprove of their bottom candidate, i.e. they approve their two first candidates.
"""
t = self.d_ballot_share_weak_voters_fanatic.copy()
if self.voting_rule in {APPROVAL, PLURALITY}:
for ranking, share in self.d_ranking_share.items():
t[ballot_one(ranking)] += share
elif self.voting_rule == ANTI_PLURALITY:
for ranking, share in self.d_ranking_share.items():
t[ballot_one_two(ranking)] += share
else:
raise NotImplementedError
return TauVector(t, voting_rule=self.voting_rule, symbolic=self.symbolic)
def tau_fanatic(self):
"""Tau-vector associated to fanatic voting.
Returns
-------
TauVector
* In Approval or Plurality, all voters approve of their top candidate only,
* In Anti-plurality, all voters vote against their bottom candidate (i.e. for the other two).
Notes
-----
In Plurality and Anti-plurality, sincere and fanatic voting are the same. They differ only in Approval.
"""
t = self.d_ballot_share_weak_voters_fanatic.copy()
for ranking, share in self.d_ranking_share.items():
if self.voting_rule in {APPROVAL, PLURALITY}:
t[ballot_one(ranking)] += share
elif self.voting_rule == ANTI_PLURALITY:
t[ballot_one_two(ranking)] += self.d_ranking_share[ranking]
else:
raise NotImplementedError
return TauVector(t, voting_rule=self.voting_rule, symbolic=self.symbolic)
def __init__(self,
d_ranking_ballot,
d_weak_order_ballot=None,
profile=None,
voting_rule=None):
"""
>>> strategy = StrategyTwelve({'non_existing_ranking': 'utility-dependent'})
Traceback (most recent call last):
ValueError: Unknown key: non_existing_ranking
>>> strategy = StrategyTwelve({'abc': 'non_existing_ballot'})
Traceback (most recent call last):
ValueError: Unknown strategy: non_existing_ballot
"""
voting_rule = self._get_voting_rule_(profile, voting_rule)
# Populate the dictionary and check for typos in the input
self.d_ranking_ballot = DictPrintingInOrderIgnoringZeros(
{ranking: ''
for ranking in RANKINGS})
for ranking, ballot in d_ranking_ballot.items():
# Sanity checks
if ranking not in RANKINGS:
raise ValueError('Unknown key: ' + ranking)
if voting_rule == APPROVAL:
authorized_ballots = {
ballot_one(ranking),
ballot_one_two(ranking),
ballot_one_two(ranking)[::-1], '', UTILITY_DEPENDENT
}
elif voting_rule == PLURALITY:
authorized_ballots = {
ballot_one(ranking),
ballot_two(ranking), '', UTILITY_DEPENDENT
}
elif voting_rule == ANTI_PLURALITY:
authorized_ballots = {
ballot_one_two(ranking),
ballot_one_two(ranking)[::-1],
ballot_one_three(ranking),
ballot_one_three(ranking)[::-1], '', UTILITY_DEPENDENT
}
else:
raise NotImplementedError
if ballot not in authorized_ballots:
raise ValueError('Unknown strategy: ' + ballot)
# Record the ballot
self.d_ranking_ballot[
ranking] = ballot if ballot == UTILITY_DEPENDENT else sort_ballot(
ballot)
# Weak orders
self.d_weak_order_ballot = DictPrintingInOrderIgnoringZeros(
{weak_order: ''
for weak_order in WEAK_ORDERS_WITHOUT_INVERSIONS})
if d_weak_order_ballot:
if voting_rule == APPROVAL:
for weak_order, ballot in d_weak_order_ballot.items():
if ballot != '':
raise ValueError(
'In Approval, you should not specify ballots for weak orders.'
)
elif voting_rule == PLURALITY:
for weak_order, ballot in d_weak_order_ballot.items():
if not is_weak_order(weak_order):
raise ValueError('Unknown key: ' + weak_order)
elif is_hater(weak_order):
possible_ballots = {
weak_order[0], weak_order[2], SPLIT
}
if ballot not in possible_ballots:
raise ValueError('Unknown strategy: ' + ballot)
self.d_weak_order_ballot[sort_weak_order(
weak_order)] = ballot
else: # is_lover(weak_order)
if ballot != '':
raise ValueError(
'In Plurality, you should not specify ballots for "lovers" (e.g. a>b~c).'
)
elif voting_rule == ANTI_PLURALITY:
for weak_order, ballot in d_weak_order_ballot.items():
if not is_weak_order(weak_order):
raise ValueError('Unknown key: ' + weak_order)
elif is_lover(weak_order):
possible_ballots = {
sort_ballot(weak_order[0] + weak_order[2]),
sort_ballot(weak_order[0] + weak_order[4]), SPLIT
}
if ballot != SPLIT:
ballot = sort_ballot(ballot)
if ballot not in possible_ballots:
raise ValueError('Unknown strategy: ' + ballot +
' for ' + weak_order)
self.d_weak_order_ballot[sort_weak_order(
weak_order)] = ballot
else: # is_hater(weak_order)
if ballot != '':
raise ValueError(
'In Anti-Plurality, you should not specify ballots '
'for "haters" (e.g. a~b>c).')
else:
raise NotImplementedError
# Call parent class
super().__init__(profile=profile, voting_rule=voting_rule)