在python中用遗传算法求解传教士和野人渡河问题并且整个问题解决过程图形化表示,并对所得图形进行分析
时间: 2024-02-06 09:10:57 浏览: 22
好的,我会尽力回答你的问题。首先,传教士和野人渡河问题是一个经典的游戏问题,目标是将三个传教士和三个野人带过河流,但是每次只能够载两个人,而且必须保证传教士的数量不少于野人的数量。遗传算法是一种优化算法,可以用来求解这类问题。
下面是Python中使用遗传算法求解传教士和野人渡河问题的代码:
```python
import random
import copy
import matplotlib.pyplot as plt
# 游戏状态类
class GameState:
def __init__(self, missionaries_left, cannibals_left, boat, missionaries_right, cannibals_right):
self.missionaries_left = missionaries_left
self.cannibals_left = cannibals_left
self.boat = boat
self.missionaries_right = missionaries_right
self.cannibals_right = cannibals_right
def is_goal(self):
return self.missionaries_left == 0 and self.cannibals_left == 0
def is_valid(self):
if self.missionaries_left >= 0 and self.missionaries_right >= 0 \
and self.cannibals_left >= 0 and self.cannibals_right >= 0 \
and (self.missionaries_left == 0 or self.missionaries_left >= self.cannibals_left) \
and (self.missionaries_right == 0 or self.missionaries_right >= self.cannibals_right):
return True
else:
return False
def __eq__(self, other):
return self.missionaries_left == other.missionaries_left and self.cannibals_left == other.cannibals_left \
and self.boat == other.boat and self.missionaries_right == other.missionaries_right \
and self.cannibals_right == other.cannibals_right
def __hash__(self):
return hash((self.missionaries_left, self.cannibals_left, self.boat, self.missionaries_right, self.cannibals_right))
# 遗传算法类
class GeneticAlgorithm:
def __init__(self, population_size, mutation_rate, generations, elite_size):
self.population_size = population_size
self.mutation_rate = mutation_rate
self.generations = generations
self.elite_size = elite_size
def init_population(self):
population = []
for i in range(self.population_size):
population.append(self.create_individual())
return population
def create_individual(self):
return [random.randint(0, 1) for _ in range(6)]
def fitness(self, individual):
game_state = self.decode_individual(individual)
return self.evaluate_game_state(game_state)
def decode_individual(self, individual):
missionaries_left = sum(individual[:3])
cannibals_left = sum(individual[3:])
boat = individual[2]
missionaries_right = 3 - missionaries_left
cannibals_right = 3 - cannibals_left
return GameState(missionaries_left, cannibals_left, boat, missionaries_right, cannibals_right)
def evaluate_game_state(self, game_state):
if not game_state.is_valid():
return 0
if not game_state.is_goal():
return 1
return 2
def select_parents(self, population):
parents = []
for i in range(2):
fitnesses = [self.fitness(individual) for individual in population]
max_fitness_index = fitnesses.index(max(fitnesses))
parents.append(population[max_fitness_index])
population.pop(max_fitness_index)
return parents
def crossover(self, parent1, parent2):
crossover_point = random.randint(1, len(parent1) - 2)
child1 = parent1[:crossover_point] + parent2[crossover_point:]
child2 = parent2[:crossover_point] + parent1[crossover_point:]
return child1, child2
def mutate(self, individual):
for i in range(len(individual)):
if random.random() < self.mutation_rate:
individual[i] = 1 - individual[i]
return individual
def evolve(self, population):
elite_size = int(self.elite_size * self.population_size)
elite = sorted(population, key=self.fitness, reverse=True)[:elite_size]
offspring_size = self.population_size - elite_size
offspring = []
for i in range(offspring_size):
parent1, parent2 = self.select_parents(population)
child1, child2 = self.crossover(parent1, parent2)
offspring.append(self.mutate(child1))
offspring.append(self.mutate(child2))
return elite + offspring
def run(self):
population = self.init_population()
fitness_history = [self.fitness(individual) for individual in population]
for i in range(self.generations):
population = self.evolve(population)
fitness_history += [self.fitness(individual) for individual in population]
return fitness_history
# 绘制图形
def plot(fitness_history):
plt.plot(list(range(len(fitness_history))), fitness_history)
plt.xlabel('Generation')
plt.ylabel('Fitness')
plt.show()
if __name__ == '__main__':
ga = GeneticAlgorithm(population_size=100, mutation_rate=0.01, generations=100, elite_size=0.2)
fitness_history = ga.run()
plot(fitness_history)
```
在上面的代码中,我们定义了`GameState`类来表示游戏状态,其中包含传教士和野人的数量以及船的位置。我们还定义了一个`GeneticAlgorithm`类来实现遗传算法。在遗传算法中,我们使用二进制编码来表示每个游戏状态,并使用`decode_individual`方法将二进制编码转换为`GameState`对象。为了评价游戏状态的适应度,我们使用`evaluate_game_state`方法来计算游戏状态的得分。在遗传算法中,我们使用选择、交叉和变异操作来生成新的个体,并使用精英选择策略来保留最适应的个体。最后,我们使用`plot`函数来绘制适应度历史曲线。
在运行上面的代码后,你将得到一个适应度历史曲线的图形。通过这个图形,你可以分析遗传算法在求解传教士和野人渡河问题中的表现。如果适应度历史曲线趋向于收敛,那么说明遗传算法能够找到一个接近最优解的解。如果适应度历史曲线不稳定或者趋向于收敛到一个较差的解,那么说明遗传算法有待改进。