遗传算法求香蕉函数的极大值

遗传算法是一种优化算法，可以用于求解函数的极大值或极小值。香蕉函数（Rosenbrock函数）是一个经典的非凸函数，常用于测试最优化算法的性能。

下面是使用遗传算法求解香蕉函数极大值的一个示例：

import random

# 定义香蕉函数
def banana_function(x1, x2):
    return (1 - x1)**2 + 100 * (x2 - x1**2)**2

# 定义遗传算法函数
def genetic_algorithm(Size, G, Codel, umax, umin, pc, pm):
    # 初始化种群
    population = []
    for _ in range(Size):
        individual = [random.uniform(umin, umax) for _ in range(Codel)]
        population.append(individual)

    # 迭代进化
    for _ in range(G):
        # 计算适应度
        fitness = [banana_function(individual[0], individual[1]) for individual in population]

        # 选择
        selected_population = []
        for _ in range(Size):
            # 轮盘赌选择
            total_fitness = sum(fitness)
            pick = random.uniform(0, total_fitness)
            current_fitness = 0
            for i in range(Size):
                current_fitness += fitness[i]
                if current_fitness > pick:
                    selected_population.append(population[i])
                    break

        # 交叉
        offspring_population = []
        for i in range(0, Size, 2):
            parent1 = selected_population[i]
            parent2 = selected_population[i+1]
            if random.random() < pc:
                # 单点交叉
                crossover_point = random.randint(1, Codel-1)
                offspring1 = parent1[:crossover_point] + parent2[crossover_point:]
                offspring2 = parent2[:crossover_point] + parent1[crossover_point:]
            else:
                offspring1 = parent1
                offspring2 = parent2
            offspring_population.append(offspring1)
            offspring_population.append(offspring2)

        # 变异
        for i in range(Size):
            individual = offspring_population[i]
            for j in range(Codel):
                if random.random() < pm:
                    individual[j] = random.uniform(umin, umax)

        # 更新种群
        population = offspring_population

    # 找到最优解
    best_individual = population[0]
    best_fitness = banana_function(best_individual[0], best_individual[1])
    for individual in population:
        fitness = banana_function(individual[0], individual[1])
        if fitness > best_fitness:
            best_individual = individual
            best_fitness = fitness

    return best_fitness, best_individual[0], best_individual[1]

# 调用遗传算法函数求解香蕉函数的极大值
BestSfi, BestS, x1, x2 = genetic_algorithm(Size=100, G=100, Codel=2, umax=5, umin=-5, pc=0.8, pm=0.01)
print("最大值：", BestSfi)
print("最优解：", BestS, x1, x2)

这段代码使用遗传算法对香蕉函数进行了优化，输出了找到的最大值和对应的最优解。