q-learning强化学习使用基础

sofu456

发布于 2023-09-21 08:43:54

2110

发布于 2023-09-21 08:43:54

文章被收录于专栏：sofu456

强化学习

通过策略的方式来学习，q-learing（马尔科夫链模型）

马尔科夫链：奖励*折扣因子，R(t)=reward(1)+yR(t+1)，马尔可夫链多次迭代后分布趋于稳定所以可以得到最优解

q-learning

构建qtable，二维数组包含两个维度，state、action，qtable迭代过程中值不大于1

-	action1	action2	action3
state1
state2
state3

action更新公式：Q(s,a)←Q(s,a)+α[reward+γmax′Q(s′,a′)−Q(s,a)] 给每个action打分，最后使用numpy的argmax得到最大值索引 γ折扣因子，值越大，当前action权重越大，否者历史action权重大

训练过程引入贪心算法

gym使用

import gym

quit = False
env = gym.make("CartPole-v1", render_mode="human")
print(env.observation_space,env.action_space)
state = env.reset()    #reset返回env内在的状态4参数，qtable的state=4个参数组成一个state值，再根据state的参数范围，划分出n个状态，action=0，1左右2个值
while not quit:
    env.render()
    env.step(1)

官方demo

env = gym.make('CartPole-v0')
for i_episode in range(20):
    observation = env.reset() #初始化环境每次迭代
    for t in range(100):
        env.render() #显示
        print(observation)
        action = env.action_space.sample() #随机选择action
        observation, reward, done, info = env.step(action)
        if done:#判断游戏是否结束
            print("Episode finished after {} timesteps".format(t+1))
            break
env.close()

q-learning

官方demo，gym的reward奖励不需要自己构建，gym会根据用户操作给出相应的reward值，step函数返回

alpha = 0.8
nstate = 50   #划分状态区间，平衡游戏只在初始位置有效，平均划分状态值不好训练
gamma = 1  #衰减因子
env = gym.make("CartPole-v0", render_mode="human")
table = np.zeros((nstate,nstate,nstate,nstate,env.action_space.n))#左右两个action
print(env.observation_space,env.action_space)

for i in range(10000):
    t=0
    observation = env.reset()
    high = env.observation_space.high
    low = env.observation_space.low
    high[1]=high[3]=10   #重新定义取值范围，否则state索引位置不变化
    low[1]=low[3]=-10   #重新定义取值范围，否则state索引位置不变化
    while True:
        env.render()
        div = (high-low)/nstate
        state = tuple(((observation[0]-env.observation_space.low)/div).astype(int))
        if np.random.random() < 0.3:#随机选择
            action = env.action_space.sample()
        else:
            action = np.argmax(table[state])
        t+=1
        observation = env.step(action)
        table[state][action] += (alpha*(observation[1]+ gamma * np.max(table[state])-table[state][action]))
        if observation[2]: 
            print("{} Episode finished after {} timesteps".format(state,t+1))
            break;

小车爬山的例子

env = gym.make("MountainCar-v0", render_mode="human")
n_states = 40
iter_max = 10000
gamma = 1.0
epsilon = 0.3
alpha = 0.5

def obs_to_state(obs):   #把参数范围划分40个状态，求当前值在哪个状态区间
    env_low = env.observation_space.low
    env_high = env.observation_space.high
    env_dx = (env_high - env_low) / n_states
    state_index = tuple(((obs - env_low) / env_dx).astype(int))
    return state_index

Q = np.zeros((n_states, n_states, env.action_space.n))
obs = env.reset()
s = obs_to_state(obs[0])
while True:
    env.render()
    if np.random.uniform(0, 1) < epsilon:
        a = env.action_space.sample()
    else:
        a = np.argmax(Q[s])
    obs = env.step(a)
    if obs[2]: break
    next_s = obs_to_state(obs[0])
    td_target = obs[1] + gamma * np.max(Q[next_s])
    td_error = td_target - Q[s][a]
    Q[s][a] += alpha * td_error
    s = next_s

print(Q)