10 CL3

 import numpy as np

import random

def distance(city1, city2):

    return np.linalg.norm(city1 - city2) 

num_cities = 4

num_ants = 4

evaporation_rate = 0.05

alpha = 1

beta = 1

cities = np.random.rand(num_cities, 2)

distances = []

for city1 in cities:

    temp = []

    for city2 in cities: 

        temp.append(distance(city1, city2))

    distances.append(temp)

phermones = np.random.rand(num_cities, num_cities)

tour_lengths = []

tour_paths = []

for _ in range(num_ants):

    randomly_selected_city = random.randint(0, num_cities-1)

    selected_city = randomly_selected_city

    tour_length = 0

    tour_path = []

    for j in range(num_cities): 

        tour_path.append(selected_city)

        dist = distances[selected_city]

        phero = phermones[selected_city]

        stochastic_gradient_descent = []

        for i in range(len(dist)):

            if dist[i] != 0: stochastic_gradient_descent.append(((phero[i])**alpha)*((1/dist[i])**beta))

            else: stochastic_gradient_descent.append(0)

        

        total_eta = sum(stochastic_gradient_descent)

        for i in range(len(stochastic_gradient_descent)):

            stochastic_gradient_descent[i]= stochastic_gradient_descent[i] / total_eta

        

        

        solution_set, temp = [], 0

        for i in range(len(stochastic_gradient_descent)):

            temp += stochastic_gradient_descent[i]

            solution_set.append(temp)

        random_value = random.random()    

        for i in range(len(solution_set)): 

            if random_value <= solution_set[i]:

                if i not in tour_path:

                    selected_city = i

                    break

        tour_length += dist[selected_city]

        for i in range(len(phero)): 

            phero[i] = (1 - evaporation_rate)*phero[i]

        phermones[selected_city] = phero

        

    tour_length += distances[randomly_selected_city][selected_city]

    tour_path.append(randomly_selected_city)   

    tour_lengths.append(tour_length)

    tour_paths.append(tour_path)

minimum_index = tour_lengths.index(min(tour_lengths))

print("Shortest Distance: ", tour_lengths[minimum_index])

print("Shortest Path: ",  tour_paths[minimum_index])