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Tournament selection improved slowest case.

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This commit is contained in:
SimpleArt
2020-12-09 11:03:04 -05:00
parent dcf14b945f
commit 4edf073f32
1 changed files with 13 additions and 8 deletions
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21
src/parent_selection/parent_selection_methods.py
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@ -77,6 +77,7 @@ class Parent_Selection:
Will make tournaments of size tournament_size and choose the winner (best fitness)
from the tournament and use it as a parent for the next generation. The total number
of parents selected is determined by parent_ratio, an attribute to the GA object.
May require many loops if the selection probability is very low.
"""
# Choose the tournament size.
@ -86,12 +87,12 @@ class Parent_Selection:
tournament_size = min(5, len(ga.population))
# Repeat tournaments until the mating pool is large enough.
while True:
while len(ga.population.mating_pool) < parent_amount:
# Generate a random tournament group and sort by fitness.
tournament_group = sorted(random.sample(
range(len(ga.population)),
k = tournament_size
tournament_size
))
# For each chromosome, add it to the mating pool based on its rank in the tournament.
@ -100,12 +101,14 @@ class Parent_Selection:
# Probability required is selection_probability * (1-selection_probability) ^ index
# 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])
if random.random() < ga.selection_probability * (1-ga.selection_probability) ** index:
break
# Stop tournament selection if enough parents are selected
if len(ga.population.mating_pool) >= parent_amount:
return
# Use random in tournament if noone wins
else:
index = random.randrange(tournament_size)
ga.population.set_parent(tournament_group[index])
@_check_selection_probability
@ -115,7 +118,9 @@ class Parent_Selection:
"""
Selects parents using the same probability approach as tournament selection,
but doesn't create tournaments. Uses random.choices with weighted values to
select parents and may produce duplicate parents.
select parents and may produce duplicate parents. Selects worse chromosomes
less than tournament selection, and may result in many duplicate best
chromosomes if the selection probability is too high.
"""
# Set the weights of each parent based on their rank.