def test_basic(tiebreaker):
utilities = np.array([
[0.0, 0.5, 1.0],
[1.0, 0.5, 1.0],
[0.0, 0.2, 0.0],
[0.0, 1.0, 0.7],
[0.3, 0.4, 0.5],
])
assert utility_winner(utilities, tiebreaker) == 2
def test_ties():
# Ties are very unlikely because of float equality
# Two-way tie between candidates 1 and 2
utilities = np.array([
[0.0, 0.5, 1.0],
[1.0, 0.5, 0.0],
[0.0, 0.5, 0.0],
[0.0, 1.0, 1.0],
[0.2, 0.0, 0.5],
])
# No tiebreaker:
assert utility_winner(utilities, tiebreaker=None) is None
# Mode 'order' should always prefer lowest candidate ID
assert utility_winner(utilities, tiebreaker='order') == 1
# Mode 'random' should choose all tied candidates at random
assert collect_random_results(utility_winner, utilities) == {1, 2}
# Three-way tie between 0, 1, and 2
utilities = np.array([
[0.0, 0.5, 1.0],
[1.0, 0.5, 0.0],
[0.0, 1.0, 0.5],
[1.0, 0.0, 0.5],
[0.5, 0.5, 0.5],
])
# No tiebreaker:
assert utility_winner(utilities, tiebreaker=None) is None
# Mode 'order' should always prefer lowest candidate ID
assert utility_winner(utilities, tiebreaker='order') == 0
# Mode 'random' should choose all tied candidates at random
assert collect_random_results(utility_winner, utilities) == {0, 1, 2}
def func():
count = defaultdict(dict)
for n_cands in n_cands_list:
utilities = random_utilities(n_voters, n_cands)
# Find the social utility winner and accumulate utilities
UW = utility_winner(utilities)
count['UW'][n_cands] = utilities.sum(axis=0)[UW]
for name, method in rated_methods.items():
try:
winner = method(utilities, tiebreaker='random')
count[name][n_cands] = utilities.sum(axis=0)[winner]
except ValueError:
# Skip junk cases like vote-for-2 with 2 candidates
count[name][n_cands] = np.nan
rankings = honest_rankings(utilities)
for name, method in ranked_methods.items():
winner = method(rankings, tiebreaker='random')
count[name][n_cands] = utilities.sum(axis=0)[winner]
return count
ranked_methods = {'Standard': fptp, 'Borda': borda}
rated_methods = {'Vote-for-half': lambda utilities, tiebreaker:
approval(vote_for_k(utilities, 'half'), tiebreaker)}
count = {key: Counter() for key in (ranked_methods.keys() |
rated_methods.keys() | {'UW'})}
start_time = time.monotonic()
for iteration in range(n):
for n_cands in n_cands_list:
utilities = random_utilities(n_voters, n_cands)
# Find the social utility winner and accumulate utilities
UW = utility_winner(utilities)
count['UW'][n_cands] += utilities.sum(axis=0)[UW]
for name, method in rated_methods.items():
winner = method(utilities, tiebreaker='random')
count[name][n_cands] += utilities.sum(axis=0)[winner]
rankings = honest_rankings(utilities)
for name, method in ranked_methods.items():
winner = method(rankings, tiebreaker='random')
count[name][n_cands] += utilities.sum(axis=0)[winner]
elapsed_time = time.monotonic() - start_time
print('Elapsed:', time.strftime("%H:%M:%S", time.gmtime(elapsed_time)), '\n')
plt.figure(f'Effectiveness, {n_voters} voters, {n} iterations')
def test_legit_winner(election, tiebreaker):
election = np.asarray(election)
n_cands = election.shape[1]
winner = utility_winner(election, tiebreaker)
assert isinstance(winner, int)
assert winner in range(n_cands)
def test_legit_winner_no_tiebreaker(election):
election = np.asarray(election)
n_cands = election.shape[1]
winner = utility_winner(election)
assert isinstance(winner, (int, type(None)))
assert winner in set(range(n_cands)) | {None}