我正在尝试运行我用 python 编写的遗传算法。不幸的是,当发生突变时,尽管使用精英主义将最适合的解决方案从上一代传递给新的解决方案,但最适合的解决方案可能比上一代的最适合解决方案更差。像这样:
There are 86825 generations left
Invalid count is: 0
The fittest individual has a fitness of 16.9094.
The least fit individual has a fitness of 36.6535
*******************************************************************************
mutation on 107
There are 86824 generations left
Invalid count is: 3
The fittest individual has a fitness of 19.8637.
The least fit individual has a fitness of 1.1618e+09
我试图实施精英主义,我认为这会避免这种情况发生,但它仍然会发生。我的算法按以下顺序执行:
NUM_GEN = 100000
print "Running Genetic Algorithm for %d generations." % NUM_GEN
gen_count = 0
while gen_count < NUM_GEN:
#genetic.add_fitness_key()
genetic.add_fitness_fast()
fittest_list = np.append(fittest_list, genetic.fittest_fitness)
least_fit_list = np.append(least_fit_list, genetic.least_fitness)
genetic.sort_pop()
genetic.make_new_pop()
genetic.elitism()
genetic.population = genetic.new_pop
print "There are %g generations left" %(NUM_GEN-gen_count)
gen_count+=1
被调用的函数是:
def select_parent_from_tournament(self):
x = random.randint(0, 19)
player1 = self.population[x]
y = random.randint(0, 19)
player2 = self.population[y]
if player1['fitness'] <= player2['fitness']:
parent = player1['chrom_list']
else:
parent = player2['chrom_list']
return parent
def crossover(self):
crossover_point = random.randint(0, self.chromosome_size)*(self.string_length)
parent1 = self.select_parent_from_tournament()
parent2 = self.select_parent_from_tournament()
parent1 = self.mutate(parent1)
parent2 = self.mutate(parent2)
child1 = parent1[:crossover_point] + parent2[crossover_point:]
child2 = parent1[crossover_point:] + parent2[:crossover_point]
return child1, child2
def mutate(self, chromosome):
for i in range(len(chromosome)):
if random.random() < self.mutation_rate:
print 'mutation on %i' % i
if chromosome[i] =='0':
chromosome[i] = '1'
else:
chromosome[i] = '0'
return chromosome
def make_new_pop(self):
self.new_pop = []
for i in range(10):
dictionary1= {}
dictionary2 = {}
dictionary1['chrom_list'], dictionary2['chrom_list'] = \
self.crossover()
self.new_pop = np.append(self.new_pop, [dictionary1, dictionary2])
def elitism(self):
r = random.randint(0, 19)
self.new_pop[r] = self.population[0]
所以我不明白为什么如果发生突变,旧人口中最适合的解决方案不会传递给新人口?