写代码用蚁群算法解决旅行商问题

以下是使用蚁群算法解决旅行商问题的Python代码：

import random
import math


class Ant:
    def __init__(self, start_city, num_cities, pheromone_matrix, distance_matrix, alpha=1.0, beta=3.0, q0=0.9):
        self.start_city = start_city
        self.current_city = start_city
        self.visited_cities = [start_city]
        self.num_cities = num_cities
        self.pheromone_matrix = pheromone_matrix
        self.distance_matrix = distance_matrix
        self.alpha = alpha
        self.beta = beta
        self.q0 = q0
    
    def select_next_city(self):
        probabilities = []
        total_prob = 0.0
        q = random.uniform(0, 1)
        if q < self.q0:
            max_prob = 0.0
            max_city = None
            for city in range(self.num_cities):
                if city not in self.visited_cities:
                    prob = self.pheromone_matrix[self.current_city][city] ** self.alpha * \
                           (1.0 / self.distance_matrix[self.current_city][city]) ** self.beta
                    if prob > max_prob:
                        max_prob = prob
                        max_city = city
            next_city = max_city
        else:
            for city in range(self.num_cities):
                if city not in self.visited_cities:
                    prob = self.pheromone_matrix[self.current_city][city] ** self.alpha * \
                           (1.0 / self.distance_matrix[self.current_city][city]) ** self.beta
                    probabilities.append((city, prob))
                    total_prob += prob
            if total_prob == 0.0:
                next_city = None
            else:
                probabilities = [(city, prob / total_prob) for city, prob in probabilities]
                next_city = self.roulette_wheel(probabilities)
        return next_city
    
    def roulette_wheel(self, probabilities):
        r = random.uniform(0, 1)
        cumulative_prob = 0.0
        for city, prob in probabilities:
            cumulative_prob += prob
            if cumulative_prob >= r:
                return city
        assert False, 'Should not reach here'
    
    def travel(self):
        while len(self.visited_cities) < self.num_cities:
            next_city = self.select_next_city()
            if next_city is None:
                break
            self.visited_cities.append(next_city)
            self.current_city = next_city
    
    def tour_length(self):
        tour_len = 0.0
        for i in range(self.num_cities):
            tour_len += self.distance_matrix[self.visited_cities[i - 1]][self.visited_cities[i]]
        return tour_len


class ACO:
    def __init__(self, num_ants, num_iterations, num_cities, distance_matrix, alpha=1.0, beta=3.0, rho=0.1, q0=0.9):
        self.num_ants = num_ants
        self.num_iterations = num_iterations
        self.num_cities = num_cities
        self.distance_matrix = distance_matrix
        self.alpha = alpha
        self.beta = beta
        self.rho = rho
        self.q0 = q0
        self.pheromone_matrix = [[1.0 / num_cities for j in range(num_cities)] for i in range(num_cities)]
    
    def run(self):
        best_tour_len = float('inf')
        best_tour = None
        for i in range(self.num_iterations):
            ants = [Ant(random.randint(0, self.num_cities - 1), self.num_cities, self.pheromone_matrix,
                        self.distance_matrix, self.alpha, self.beta, self.q0) for j in range(self.num_ants)]
            for ant in ants:
                ant.travel()
                tour_len = ant.tour_length()
                if tour_len < best_tour_len:
                    best_tour_len = tour_len
                    best_tour = ant.visited_cities
                for i in range(self.num_cities):
                    j = (i + 1) % self.num_cities
                    self.pheromone_matrix[ant.visited_cities[i]][ant.visited_cities[j]] *= 1.0 - self.rho
                    self.pheromone_matrix[ant.visited_cities[i]][ant.visited_cities[j]] += self.rho / tour_len
        return best_tour, best_tour_len


if __name__ == '__main__':
    # Example usage
    num_cities = 10
    coords = []
    for i in range(num_cities):
        x = random.uniform(0, 1)
        y = random.uniform(0, 1)
        coords.append((x, y))
    distance_matrix = [[0.0 for j in range(num_cities)] for i in range(num_cities)]
    for i in range(num_cities):
        for j in range(num_cities):
            if i != j:
                dx = coords[i][0] - coords[j][0]
                dy = coords[i][1] - coords[j][1]
                distance_matrix[i][j] = math.sqrt(dx ** 2 + dy ** 2)
    aco = ACO(num_ants=10, num_iterations=100, num_cities=num_cities, distance_matrix=distance_matrix)
    best_tour, best_tour_len = aco.run()
    print('Best tour:', best_tour)
    print('Best tour length:', best_tour_len)

该代码通过随机生成城市坐标，并计算两两城市之间的距离来构造旅行商问题的数据。然后使用蚁群算法来寻找最优解，其中包括了Ant和ACO两个类，分别实现了蚂蚁和蚁群算法的相关操作。最终输出最优解及其长度。