📅  最后修改于: 2023-12-03 15:11:27.563000             🧑  作者: Mango
稳态遗传算法 (SSGA) 是一种基于进化算法的优化方法,适用于解决各类复杂问题。相较于传统遗传算法,SSGA 更加高效,能够快速找到优化问题的最优解。
SSGA 的核心思想是利用遗传算法的三个基本操作:选择、交叉、变异。不同的是,SSGA 采用的是“稳态”进化模型,即在每次进化中只替换掉一部分种群,而不是整个种群。该算法的演化过程如下:
其中,SSGA 还引入了"多样性维持策略",以确保不陷入局部最优解。多样性维持策略主要有以下几种:
以下是简单的 SSGA 代码实现:
import random
def init_population(pop_num, chrom_len):
"""初始化种群"""
population = []
for i in range(pop_num):
chromosome = [random.randint(0,1) for j in range(chrom_len)]
population.append(chromosome)
return population
def fitness_function(chromosome):
"""适应度函数"""
return sum(chromosome)
def select(population, parents_num):
"""选择操作"""
conf_fitness = [fitness_function(chromosome) for chromosome in population]
chosen = random.choices(list(enumerate(population)), conf_fitness, k=parents_num)
parents = [chromosome for index, chromosome in chosen]
return parents
def crossover(parents, pc):
"""交叉操作"""
children = []
for i in range(0, len(parents), 2):
if i+1 >= len(parents):
break
p1, p2 = parents[i], parents[i+1]
if random.random() < pc:
pos = random.randint(0, len(p1))
child1 = p1[:pos] + p2[pos:]
child2 = p2[:pos] + p1[pos:]
children.append(child1)
children.append(child2)
return children
def mutation(children, pm):
"""变异操作"""
for child in children:
for j in range(len(child)):
if random.random() < pm:
child[j] = 1 - child[j]
def insert(population, offspring):
"""替换操作"""
conf_fitness = [fitness_function(chromosome) for chromosome in population]
fitness_sorted = sorted(list(enumerate(conf_fitness)), key=lambda x: x[1], reverse=True)
if fitness_sorted[-1][1] < fitness_function(offspring):
population[fitness_sorted[0][0]] = offspring
def run_SSGA(pop_num, chrom_len, pc, pm, max_gen):
"""SSGA运行过程"""
population = init_population(pop_num, chrom_len)
for i in range(max_gen):
parents = select(population, int(pop_num/2))
children = crossover(parents, pc)
mutation(children, pm)
new_population = population[int(pop_num/2):] + children
for offspring in new_population:
insert(population, offspring)
conf_fitness = [fitness_function(chromosome) for chromosome in population]
max_index = conf_fitness.index(max(conf_fitness))
return population[max_index]
chrom_len = 10 # 染色体长度
pop_num = 50 # 种群中个体数
pc = 0.8 # 交叉概率
pm = 0.1 # 变异概率
max_gen = 100 # 最大迭代次数
best_chromosome = run_SSGA(pop_num, chrom_len, pc, pm, max_gen)
print(best_chromosome)
该代码演示了一个简单的 SSGA 实现,包含了种群初始化、适应度函数、选择、交叉、变异、替换等操作。请注意,该代码是具有一定简化的,实际使用中还需要对算法的参数等进行优化。
稳态遗传算法是一种高效稳定的进化算法,能够解决各类优化问题,并且还能够引入多样性维持策略,确保不陷入局部最优解。在实际应用中,开发人员可以针对具体问题选用并对算法参数进行调优,从而取得更好的效果。