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Added cleaner comments to explain.

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SimpleArt
2020-12-02 18:00:23 -05:00
parent 1761092abb
commit bfe4699513
1 changed files with 13 additions and 4 deletions
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17
src/parent_selection/parent_selection_methods.py
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@ -98,10 +98,8 @@ class Parent_Selection:
for index in range(tournament_size):
# Probability required is selection_probability * (1-selection_probability) ^ index
# e.g. top ranked fitness has probability: selection_probability
# second ranked fitness has probability: selection_probability * (1-selection_probability)
# third ranked fitness has probability: selection_probability * (1-selection_probability)^2
# etc.
# Each chromosome is (1-selection_probability) times
# more likely to become a parent than the next ranked.
if random.random() < ga.selection_probability * pow(1-ga.selection_probability, index):
ga.population.set_parent(tournament_group[index])
@ -120,12 +118,16 @@ class Parent_Selection:
select parents and may produce duplicate parents.
"""
# Set the weights of each parent based on their rank.
# Each chromosome is (1-selection_probability) times
# more likely to become a parent than the next ranked.
weights = [
(1-ga.selection_probability) ** i
for i
in range(len(ga.population))
]
# Set the mating pool.
ga.population.mating_pool = random.choices(ga.population, weights, k = parent_amount)
@ -183,17 +185,24 @@ class Parent_Selection:
weighted values to select parents and may produce duplicate parents.
"""
# All fitnesses are the same, select randomly.
if ga.get_chromosome_fitness(-1) == ga.get_chromosome_fitness(0):
offset = 1-ga.get_chromosome_fitness(-1)
# Some chromosomes have negative fitness, shift them all into positives.
elif ga.get_chromosome_fitness(-1) < 0:
offset = -ga.get_chromosome_fitness(-1)
# No change needed.
else:
offset = 0
# Set the weights of each parent based on their fitness + offset.
weights = [
ga.get_chromosome_fitness(index) + offset
for index
in range(len(ga.population))
]
# Set the mating pool.
ga.population.mating_pool = random.choices(ga.population, weights, k = parent_amount)