24/8/17算法笔记 策略梯度reinforce算法
import gym
from matplotlib import pyplot as plt
%matplotlib inline#创建环境
env = gym.make('CartPole-v0')
env.reset()#打印游戏
def show():plt.imshow(env.render(mode = 'rgb_array'))plt.show()
show()
定义网络模型
import torch
#定义模型
model = torch.nn.Sequential(torch.nn.Linear(4,128),torch.nn.ReLU(),torch.nn.Linear(128,2),torch.nn.Softmax(dim=1),
)
model(torch.randn(2,4))定义动作函数
import random
#得到一个动作
def get_action(state):state = torch.FloatTensor(state).reshape(1,4)#[1,4]->[1,2]prob = model(state)#根据概率选择一个动作action = random.choice(range(2),weights = prob[0].tolist(),k=1)[0]
#这行代码从 0 到 1（包含）的整数范围内选择一个元素作为动作，选择的概率由 prob[0] 列表中元素的值决定。return action获取一局游戏数据
def get_data():states = []rewards = []actions = []#初始化游戏state = env.reset()#玩到游戏结束为止over = Falsewhile not over:#根据当前状态得到一个动作action = get_action(state)#执行动作，得到反馈next_state,reward,over,_ = env.step(action)#记录数据样本states.append(state)rewards.append(reward)actions.append(action)#更新游戏状态，开始下一个动作state = next.statereturn states,rewards,actions
测试函数
from IPython import displaydef test(play):#初始化游戏state = env.reset()#记录反馈值的和，这个值越大越好reward_sum=0#玩到游戏结束为止over = False while not over:#根据当前状态得到一个动作action = get_action(state)#执行动作，得到反馈state,reward,over,_ = env.state(action)reward_sum += reward#打印动画if play and random.random()<0.2:#跳帧display.clear_output(wait=True) #用于清除 Jupyter Notebook 单元格的输出。show()return reward_sum训练函数
def train():optimizer = torch.optim.Adam(model.parameters(),lr = 1e-3)#玩N局游戏，得到数据states,rewards,actions = get_data()optimizer.zero_grad()#反馈的和，初始化为0reward_sum = 0#从最后一步算起for i in reversed(range(len(states))):#反馈的和，从最后一步的反馈开始计算#每往前一步，>>和<<都衰减0.02，然后再加上当前的反馈reward_sum*=0.98reward_sum+=rewards[i]#重新计算对应动作的概率state = torch.FloatTensor(states[i]).reshape(1,4)#[1,4]->[1,2]prob = model(state)#[1,2]->scalapron = pron[0,actions[i]]#根据求导公式，符号取反是因为这里是求loss,所以优化方向相反loss =-prob.log()*reward_sum#累积梯度loss.backward(retain_graph=True)optimizer.step()if epoch%100==0:test_result = sum([test(play=False) for _ in range(10)])/10print(epoch,test_result)