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一、基本步骤

遗传算法求解旅行商问题（TSP）的一般步骤如下：

1. 编码：

   • 通常采用整数编码，将城市的访问顺序表示为一个染色体。例如，假设有 5 个城市，编码为[1, 3, 5, 2, 4]，表示旅行商的访问顺序为城市 1、城市 3、城市 5、城市 2、城市 4，最后回到出发城市 1。

2. 初始化种群：

   • 随机生成一定数量的染色体，作为初始种群。

3. 适应度评估：

   • 计算每个染色体所代表的路径长度，路径长度越短，适应度越高。适应度函数可以是路径长度的倒数或其他与路径长度相关的函数。

4. 选择操作：

   • 基于适应度，选择一定比例的染色体进入下一代种群。常见的选择方法有轮盘赌选择、锦标赛选择等。

5. 交叉操作：

   • 对选中的染色体进行交叉，生成新的染色体。例如，单点交叉，随机选择一个交叉点，交换两个染色体在交叉点之后的部分。

6. 变异操作：

   • 以一定的概率对染色体中的基因进行变异，例如随机交换两个城市的位置。

7. 重复步骤 3 - 6 ，直到满足终止条件（如达到预定的迭代次数或找到满意的解）。

通过不断迭代，种群中的染色体逐渐优化，最终得到较优的 TSP 路径。需要注意的是，遗传算法的参数（如种群大小、交叉概率、变异概率等）需要根据具体问题进行调整和优化，以获得更好的求解效果。

二、代码

#!/usr/bin/env python
# coding: utf-8# In[32]:import numpy as np
import copy
import matplotlib
import matplotlib.pyplot as plt
from matplotlib.pyplot import MultipleLocator
import random# In[33]:#准备好距离矩阵
city_num = 5
city_dist_mat = np.zeros([city_num, city_num])
city_dist_mat[0][1] = city_dist_mat[1][0] = 1165
city_dist_mat[0][2] = city_dist_mat[2][0] = 1462
city_dist_mat[0][3] = city_dist_mat[3][0] = 3179
city_dist_mat[0][4] = city_dist_mat[4][0] = 1967
city_dist_mat[1][2] = city_dist_mat[2][1] = 1511
city_dist_mat[1][3] = city_dist_mat[3][1] = 1942
city_dist_mat[1][4] = city_dist_mat[4][1] = 2129
city_dist_mat[2][3] = city_dist_mat[3][2] = 2677
city_dist_mat[2][4] = city_dist_mat[4][2] = 1181
city_dist_mat[3][4] = city_dist_mat[4][3] = 2216
#标号说明
#list_city = ['0_北京', '1_西安', '2_上海', '3_昆明', '4_广州']# In[34]:#1.定义个体类，包括基因（城市路线）和适应度
num_person_idx = 0
num_person = 0
dis_list = []
class Individual:def __init__(self, genes = None):global num_personglobal dis_listglobal num_person_idxnum_person_idx += 1if num_person_idx % 20 == 0:num_person += 1self.genes = genesif self.genes == None:genes = [0]*5temp = [0]*4temp = [i for i in range(1,city_num)]########################################################################random.shuffle(temp)genes[1:] = tempgenes[0] = 0self.genes = genesself.fitness = self.evaluate_fitness()else:self.fitness = float(self.evaluate_fitness())#2. #计算个体的适应度def evaluate_fitness(self):dis = 0for i in range(city_num - 1):dis += city_dist_mat[self.genes[i]][self.genes[i+1]]if i == city_num - 2:dis += city_dist_mat[self.genes[i + 1]][0]#回到0if num_person_idx % 20 == 0:dis_list.append(dis)return 1/dis# In[35]:def copy_list(old):new = []for element in old:new.append(element)return new
def sort_win_num(group):for i in range(len(group)):for j in range(len(group) - i - 1):
#             print('group[j].fitness_type', type(group[j].fitness))if group[j].fitness < group[j+1].fitness:temp = group[j]group[j] = group[j+1]group[j+1] = tempreturn group
#定义Ga类 
#3~5，交叉、变异、更新种群，全部在Ga类中实现
class Ga:#input_为城市间的距离矩阵def __init__(self, input_):#声明一个全局变量global city_dist_matcity_dist_mat = input_#当代的最佳个体########################################此处做了更改#self.best = Noneself.best = Individual(None)
#         print("BBBBBBbest.fitness",self.best.fitness)#种群self.individual_list = []#每一代的最佳个体self.result_list = []#每一代个体对应的最佳适应度self.fitness_list = []#交叉,这里采用交叉变异def cross(self):new_gen = []#随机选取一段，含有num_cross个数字（城市）num_cross = 3#后期可能需要调试的参数,考虑到实际问题里只有5个城市，所以认为3较为合适for i in range(0, len(self.individual_list) - 1, 2):parent_gen1 = copy_list(self.individual_list[i].genes)parent_gen2 = copy_list(self.individual_list[i+1].genes)
#             print("parent_gen1",parent_gen1)
#             print("parent_gen2",parent_gen2)     index1_1 = 0index1_2 = 0index2_1 = 0index2_2 = 0#定义一个下表列表index_list = [0]*3for i in range(city_num - 3):#就是2，即0，1index_list[i] = i + 1index1_1 = random.choice(index_list)index1_2 = index1_1 + 2index2_1 = random.choice(index_list)index2_2 = index2_1 + 2choice_list1 = parent_gen1[index1_1:index1_2 + 1]choice_list2 = parent_gen2[index2_1:index2_2 + 1]
#             print("choice_list1",choice_list1)
#             print("choice_list2",choice_list2)#利用这一段生成两个子代,下面的赋值只是为了获取长度，所以用哪个父代能可以#也可以直接用city_num直接代替son_gen1 = [0]*city_numson_gen2 = [0]*city_num
#             print('son_gen1_size = ',len(son_gen1))
#             print('son_gen2_size = ',len(son_gen2))
#             print("index1_1 == ",index1_1)
#             print("index1_2 == ",index1_2)
#             print("index2_1 == ",index2_1)
#             print("index2_2 == ",index2_2)#找到之后进行交叉，分别得到son_gen1,son_gen2#先把选中的段复制进去son_gen1[index1_1: index1_2 + 1] = choice_list1son_gen2[index2_1: index2_2 + 1] = choice_list2
#             print("now,  son_gen1 = ", son_gen1)
#             print("now,  son_gen2 = ", son_gen2)#然后左、右“查漏补缺”temp1 = choice_list1temp2 = choice_list2if index1_1 == 0:passelse: for i in range(index1_1):for j in range(city_num):#如果父代2里面的这个当初没被选中，那就加入son_gene1if parent_gen2[j] not in choice_list1:son_gen1[i] = parent_gen2[j]#这个时候要扩增choice_list1, 这样parent_gen2里面未被选中的元素才会一个个被遍历到#1choice_list1.append(parent_gen2[j])#找到之后马上break，防止被覆盖breakchoice_list1 = temp1if index1_2 == city_num - 1:passelse:for i in range(index1_2 + 1, city_num):for j in range(city_num):if parent_gen2[j] not in choice_list1:son_gen1[i] = parent_gen2[j]#这个时候要扩增choice_list1, 这样parent_gen2里面未被选中的元素才会一个个被遍历到#2choice_list1.append(parent_gen2[j])#找到之后马上break，防止被覆盖break#son_gen2亦是如此if index2_1 == 0:passelse:for i in range(index2_1):for j in range(city_num):#如果父代1里面的这个当初没被选中，那就加入son_gen2if parent_gen1[j] not in choice_list2:son_gen2[i] = parent_gen1[j]#这个时候要扩增choice_list2, 这样parent_gen1里面未被选中的元素才会一个个被遍历到#3choice_list2.append(parent_gen1[j])#找到之后马上break，防止被覆盖breakchoice_list2 = temp2if index2_2 == city_num - 1:passelse:for i in range(index2_2 + 1, city_num):for j in range(city_num):if parent_gen1[j] not in choice_list2:
#                             print("i == ", i)son_gen2[i] = parent_gen1[j]#这个时候要扩增choice_list2, 这样parent_gen1里面未被选中的元素才会一个个被遍历到#4choice_list2.append(parent_gen1[j])#找到之后马上break，防止被覆盖break#新生成的子代基因加入new_gene列表
#             print('son_gen1 = ',son_gen1)
#             print('son_gen2 = ',son_gen2)new_gen.append(Individual(son_gen1))#print('new_gen[-1].genes', new_gen[-1].genes)new_gen.append(Individual(son_gen2))return new_gen#变异def mutate(self, new_gen):mutate_p = 0.02#待调参数index_list = [0]*(city_num-1)index_1 = 1index_2 = 1for i in range(city_num - 1):index_list[i] = i + 1for individual in new_gen:if random.random() < mutate_p:
#                 change += 1#如果变异，采用基于位置的变异,方便起见，直接使用上面定义的index列表index_l = random.choice(index_list)
#                 index_2 = (index_1 + 2) % city_num#这里让间隔为2的两个城市进行交换index_2 = random.choice(index_list)while index_1 == index_2:index_2 = random.choice(index_list)#交换temp = individual.genes[index_1]individual.genes[index_1] = individual.genes[index_2]individual.genes[index_2] = temp#变异结束，与老一代的进行合并self.individual_list += new_gen#选择def select(self):#在此选用轮盘赌算法#考虑到5的阶乘是120，所以可供选择的个体基数应该适当大一些，#在此每次从种群中选择6个，进行轮盘赌，初始化60个个体，同时适当调高变异的概率select_num = 6select_list = []for i in range(select_num):gambler = random.choice(self.individual_list)gambler = Individual(gambler.genes)select_list.append(gambler)#求出这些fitness之和sum = 0for i in range(select_num):sum += select_list[i].fitnesssum_m = [0]*select_num#实现概率累加for i in range(select_num):for j in range(i+1):sum_m[i] += select_list[j].fitnesssum_m[i] /= sumnew_select_list = []p_num = 0#随机数for i in range(select_num):p_num = random.uniform(0,1)if p_num>0 and p_num < sum_m[0]:new_select_list.append(select_list[0])elif p_num>= sum_m[0] and p_num < sum_m[1]:new_select_list.append(select_list[1])elif p_num >= sum_m[1] and p_num < sum_m[2]:new_select_list.append(select_list[2])elif p_num >= sum_m[2] and p_num < sum_m[3]:new_select_list.append(select_list[3])elif p_num >= sum_m[3] and p_num < sum_m[4]:new_select_list.append(select_list[4])elif p_num >= sum_m[4] and p_num < sum_m[5]:new_select_list.append(select_list[5])else:pass#将新生成的一代替代父代种群self.individual_list = new_select_list#更新种群def next_gen(self):#交叉new_gene = self.cross()#变异self.mutate(new_gene)#选择self.select()#获得这一代的最佳个体
#         print("**************************************")
#         print('self.best.fitness = ', self.best.fitness)
#         print('now, best.fitness = ', self.best.fitness)for individual in self.individual_list:if individual.fitness > self.best.fitness:self.best = individual
#                 print("更换了最优路径")
#                 print('now, best.fitness = ', self.best.fitness)def train(self):#随机出初代种群#individual_num = 60self.individual_list = [Individual() for _ in range(individual_num)]#迭代gen_num = 100for i in range(gen_num):#从当代种群中交叉、变异、选择出适应度最佳的个体，获得子代产生新的种群self.next_gen()#连接首位
#             print("i = ", i)result = copy.deepcopy(self.best.genes)result.append(result[0])self.result_list.append(result)self.fitness_list.append(self.best.fitness)print(self.result_list[-1])print('距离总和是：', 1/self.fitness_list[-1])
#         return self.result_list, self.fitness_listdef draw(self):x_list = [i for i in range(num_person)]y_list = dis_listplt.rcParams['figure.figsize'] = (60, 45)plt.plot(x_list, y_list, color = 'g')plt.xlabel('Cycles',size = 50)plt.ylabel('Route',size = 50)x = np.arange(0, 910, 20)y = np.arange(7800, 12000, 100)plt.xticks(x)plt.yticks(y)plt.title('Trends in distance changes', size = 50)plt.tick_params(labelsize=30)
#         plt.savefig("D:\AI_pictures\遗传算法求解TSP问题_1_轮盘赌算法")plt.show()
route = Ga(city_dist_mat)
route.train()
route.draw()