def test_tournament_selection2():
"""If there are just two individuals in the population, and we set select_worst=True,
then binary tournament selection will select the worse one with 75% probability."""
# Make a population where binary tournament_selection has an obvious
# reproducible choice
pop = [
Individual(np.array([0, 0, 0]), problem=MaxOnes()),
Individual(np.array([1, 1, 1]), problem=MaxOnes())
]
# Assign a unique identifier to each individual
pop[0].id = 0
pop[1].id = 1
# We first need to evaluate all the individuals so that
# selection has fitnesses to compare
pop = Individual.evaluate_population(pop)
selected = ops.tournament_selection(pop, select_worst=True)
N = 1000
p_thresh = 0.1
observed_dist = statistical_helpers.collect_distribution(
lambda: next(selected).id, samples=N)
expected_dist = {pop[0].id: 0.75 * N, pop[1].id: 0.25 * N}
print(f"Observed: {observed_dist}")
print(f"Expected: {expected_dist}")
assert (statistical_helpers.stochastic_equals(expected_dist,
observed_dist,
p=p_thresh))
def test_tournament_selection_indices():
"""If an empty list is provided to tournament selection, it should be populated with
the index of the selected individual.
If we select a second individual, the list should be cleared and populated with the
index of the second individual."""
pop = test_population
indices = []
op = ops.tournament_selection(indices=indices)
# Select an individual
s = next(op(pop))
# Ensure the returned index is correct
assert (len(indices) == 1)
idx = indices[0]
assert (idx >= 0)
assert (idx < len(pop))
assert (pop[idx] is s)
# Select another individual
s = next(op(pop))
# Ensure the returned index is correct
assert (len(indices) == 1)
idx = indices[0]
assert (idx >= 0)
assert (idx < len(pop))
assert (pop[idx] is s)
def test_tournament_selection():
""" This simple binary tournament_selection selection """
# Make a population where binary tournament_selection has an obvious reproducible choice
pop = [
Individual([0, 0, 0], decoder=IdentityDecoder(), problem=MaxOnes()),
Individual([1, 1, 1], decoder=IdentityDecoder(), problem=MaxOnes())
]
# We first need to evaluate all the individuals so that truncation selection has fitnesses to compare
pop = Individual.evaluate_population(pop)
best = next(ops.tournament_selection(pop))
pass
problem=problem, # Fitness function
# Stopping condition: we stop when fitness or diversity drops below a threshold
stop=lambda pop: (max(pop).fitness < fitness_threshold)
or (probe.pairwise_squared_distance_metric(pop) < diversity_threshold),
# Representation
representation=Representation(
# Initialize a population of integer-vector genomes
initialize=create_real_vector(
bounds=[problem.bounds] * l)
),
# Operator pipeline
pipeline=[
ops.tournament_selection(k=2),
ops.clone,
# Apply binomial mutation: this is a lot like
# additive Gaussian mutation, but adds an integer
# value to each gene
mutate_gaussian(std=0.2, hard_bounds=[problem.bounds]*l,
expected_num_mutations=1),
ops.evaluate,
ops.pool(size=pop_size),
# Some visualization probes so we can watch what happens
probe.CartesianPhenotypePlotProbe(
xlim=problem.bounds,
ylim=problem.bounds,
contours=problem),
probe.FitnessPlotProbe(),