表格型方法存储的状态数量有限，当面对围棋或机器人控制这类有数不清的状态的环境时，表格型方法在存储和查找效率上都受局限，DQN的提出解决了这一局限，使用神经网络来近似替代Q表格。
本质上DQN还是一个Q-learning算法，更新方式一致。为了更好的探索环境，同样的也采用epsilon-greedy方法训练。
在Q-learning的基础上，DQN提出了两个技巧使得Q网络的更新迭代更稳定。
经验回放(Experience Replay): 使用一个经验池存储多条经验s,a,r,s'，再从中随机抽取一批数据送去训练。
固定目标(Fixed Q-Target): 复制一个和原来Q网络结构一样的Target-Q网络，用于计算Q目标值。
公众号算法美食屋后台回复关键词：torchkeras，获取本文notebook源码~
不了解强化学习的同学，推荐先阅读：Q-learning解决悬崖问题
一，准备环境
gym是一个常用的强化学习测试环境，可以用make创建环境。
env具有reset,step,render几个方法。
倒立摆问题
环境设计如下：
倒立摆问题环境的状态是无限的，用一个4维的向量表示state.
4个维度分别代表如下含义
cart位置：-2.4 ~ 2.4
cart速度：-inf ~ inf
pole角度：-0.5 ～ 0.5 （radian）
pole角速度：-inf ~ inf
智能体设计如下：
智能体的action有两种，可能的取值2种：
0，向左
1，向右
奖励设计如下：
每维持一个步骤，奖励+1，到达200个步骤，游戏结束。
所以最高得分为200分。
倒立摆问题希望训练一个智能体能够尽可能地维持倒立摆的平衡。
import gym
import numpy as np
import pandas as pd
import time
import matplotlib
import matplotlib.pyplot as plt
from IPython import display
print("gym.__version__=",gym.__version__)
%matplotlib inline
#可视化函数：
def show_state(env, step, info=''):
plt.figure(num=10086,dpi=100)
plt.clf()
plt.imshow(env.render())
plt.title("step: %d %s" % (step, info))
plt.axis('off')
display.clear_output(wait=True)
display.display(plt.gcf())
plt.close()
env = gym.make('CartPole-v1',render_mode="rgb_array") # CartPole-v0: 预期最后一次评估总分 > 180（最大值是200）
env.reset()
action_dim = env.action_space.n # CartPole-v0: 2
obs_shape = env.observation_space.shape # CartPole-v0: (4,)gym.__version__= 0.26.2env.reset()
done = False
step = 0
while not done:
action = np.random.randint(0, 1)
state,reward,done,truncated,info = env.step(action)
step+=1
print(state,reward)
time.sleep(1.0)
#env.render()
show_state(env,step=step)
#print('step {}: action {}, state {}, reward {}, done {}, truncated {}, info {}'.format(\
# step, action, state, reward, done, truncated,info))
display.clear_output(wait=True)
可以看到，没有训练智能体之前，我们采取随机动作的话，只维持了10步，倒立摆就因为倾斜角度超出范围而导致游戏结束。😭
二，定义Agent
DQN的核心思想为使用一个神经网络来近似替代Q表格。
Model: 模型结构, 负责拟合函数 Q(s,a)。主要实现forward方法。
Agent:智能体，负责学习并和环境交互, 输入输出是numpy.array形式。有sample(单步采样), predict(单步预测), 有predict_batch(批量预测), compute_loss(计算损失), sync_target(参数同步)等方法。
import torch
from torch import nn
import torch.nn.functional as F
import copy
class Model(nn.Module):
def __init__(self, obs_dim, action_dim):
# 3层全连接网络
super(Model, self).__init__()
self.obs_dim = obs_dim
self.action_dim = action_dim
self.fc1 = nn.Linear(obs_dim,32)
self.fc2 = nn.Linear(32,16)
self.fc3 = nn.Linear(16,action_dim)
def forward(self, obs):
# 输入state，输出所有action对应的Q，[Q(s,a1), Q(s,a2), Q(s,a3)...]
x = self.fc1(obs)
x = torch.tanh(x)
x = self.fc2(x)
x = torch.tanh(x)
Q = self.fc3(x)
return Q
model = Model(4,2)
model_target = copy.deepcopy(model)
model.eval()
model.forward(torch.tensor([[0.2,0.1,0.2,0.0],[0.3,0.5,0.2,0.6]]))
model_target.eval()
model_target.forward(torch.tensor([[0.2,0.1,0.2,0.0],[0.3,0.5,0.2,0.6]]))tensor([[-0.1148, 0.0068],
[-0.1311, 0.0315]], grad_fn=<AddmmBackward0>)import torch
from torch import nn
import copy
class DQNAgent(nn.Module):
def __init__(self, model,
gamma=0.9,
e_greed=0.1,
e_greed_decrement=0.001
):
super().__init__()
self.model = model
self.target_model = copy.deepcopy(model)
self.gamma = gamma # reward 的衰减因子，一般取 0.9 到 0.999 不等
self.e_greed = e_greed # 有一定概率随机选取动作，探索
self.e_greed_decrement = e_greed_decrement # 随着训练逐步收敛，探索的程度慢慢降低
self.global_step = 0
self.update_target_steps = 200 # 每隔200个training steps再把model的参数复制到target_model中
def forward(self,obs):
return self.model(obs)
@torch.no_grad()
def predict_batch(self, obs):
""" 使用self.model网络来获取 [Q(s,a1),Q(s,a2),...]
"""
self.model.eval()
return self.forward(obs)
#单步骤采样
def sample(self, obs):
sample = np.random.rand() # 产生0~1之间的小数
if sample < self.e_greed:
action = np.random.randint(self.model.action_dim) # 探索：每个动作都有概率被选择
else:
action = self.predict(obs) # 选择最优动作
self.e_greed = max(
0.01, self.e_greed - self.e_greed_decrement) # 随着训练逐步收敛，探索的程度慢慢降低
return action
#单步骤预测
def predict(self, obs): # 选择最优动作
obs = np.expand_dims(obs, axis=0)
tensor = torch.tensor(obs,dtype=torch.float32).to(self.model.fc1.weight.device)
pred_Q = self.predict_batch(tensor)
action = torch.argmax(pred_Q,1,keepdim=True).cpu().numpy()
action = np.squeeze(action)
return action
def sync_target(self):
""" 把 self.model 的模型参数值同步到 self.target_model
"""
self.target_model.load_state_dict(self.model.state_dict())
def compute_loss(self, obs, action, reward, next_obs, done):
# 每隔200个training steps同步一次model和target_model的参数
if self.global_step % self.update_target_steps == 0:
self.sync_target()
self.global_step += 1
# 从target_model中获取 max Q' 的值，用于计算target_Q
self.target_model.eval()
next_pred_value = self.target_model(next_obs)
best_value = torch.max(next_pred_value, dim = 1,keepdim=True).values
target = reward.reshape((-1,1)) + (
torch.tensor(1.0) - done.reshape(-1,1)) * self.gamma * best_value
#print("best_value",best_value.shape)
#print("target",target.shape)
# 获取Q预测值
self.model.train()
pred_value = self.model(obs)
action_onehot = F.one_hot(action.reshape(-1),
num_classes = self.model.action_dim).float()
prediction = torch.sum(pred_value*action_onehot,dim= 1,keepdim=True)
#print("pred_value",pred_value.shape)
#print("action_onehot",action_onehot.shape)
#print("prediction",prediction.shape)
# 计算 Q(s,a) 与 target_Q的均方差，得到loss
loss = F.smooth_l1_loss(target,prediction)
return lossagent = DQNAgent(model,gamma=0.9,e_greed=0.1,
e_greed_decrement=0.001)agent.predict_batch(torch.tensor([[2.0,3.0,4.0,2.0],[1.0,2.0,3.0,4.0]]))tensor([[-0.1596, -0.0481],
[-0.0927, 0.0318]])loss = agent.compute_loss(torch.tensor([[2.0,3.0,4.0,2.0],[1.0,2.0,3.0,4.0],[1.0,2.0,3.0,4.0]]),
torch.tensor([[1],[0],[0]]),
torch.tensor([[1.0],[1.0],[1.0]]),
torch.tensor([[2.0,3.0,0.4,2.0],[1.0,2.0,3.0,4.0],[1.0,2.0,3.0,4.0]]),
torch.tensor(0.9))
print(loss)tensor(0.5757, grad_fn=<SmoothL1LossBackward0>)三，训练Agent
import random
import collections
import numpy as np
LEARN_FREQ = 5 # 训练频率，不需要每一个step都learn，攒一些新增经验后再learn，提高效率
MEMORY_SIZE = 2048 # replay memory的大小，越大越占用内存
MEMORY_WARMUP_SIZE = 512 # replay_memory 里需要预存一些经验数据，再开启训练
BATCH_SIZE = 128 # 每次给agent learn的数据数量，从replay memory随机里sample一批数据出来#经验回放
class ReplayMemory(object):
def __init__(self, max_size):
self.buffer = collections.deque(maxlen=max_size)
# 增加一条经验到经验池中
def append(self, exp):
self.buffer.append(exp)
# 从经验池中选取N条经验出来
def sample(self, batch_size):
mini_batch = random.sample(self.buffer, batch_size)
obs_batch, action_batch, reward_batch, next_obs_batch, done_batch = [], [], [], [], []
for experience in mini_batch:
s, a, r, s_p, done = experience
obs_batch.append(s)
action_batch.append(a)
reward_batch.append(r)
next_obs_batch.append(s_p)
done_batch.append(done)
return np.array(obs_batch).astype('float32'), \
np.array(action_batch).astype('int64'), np.array(reward_batch).astype('float32'),\
np.array(next_obs_batch).astype('float32'), np.array(done_batch).astype('float32')
def __len__(self):
return len(self.buffer)from torch.utils.data import IterableDataset,DataLoader
class MyDataset(IterableDataset):
def __init__(self,env,agent,rpm,stage='train',size=200):
self.env = env
self.agent = agent
self.rpm = rpm if stage=='train' else None
self.stage = stage
self.size = size
def __iter__(self):
obs,info = self.env.reset() # 重置环境, 重新开一局（即开始新的一个episode）
step = 0
batch_reward_true = [] #记录真实的reward
while True:
step += 1
action = self.agent.sample(obs)
next_obs, reward, done, _, _ = self.env.step(action) # 与环境进行一个交互
batch_reward_true.append(reward)
if self.stage=='train':
self.rpm.append((obs, action, reward, next_obs, float(done)))
if (len(rpm) > MEMORY_WARMUP_SIZE) and (step % LEARN_FREQ == 0):
#yield batch_obs, batch_action, batch_reward, batch_next_obs,batch_done
yield self.rpm.sample(BATCH_SIZE),sum(batch_reward_true)
batch_reward_true.clear()
else:
obs_batch = np.array([obs]).astype('float32')
action_batch = np.array([action]).astype('int64')
reward_batch = np.array([reward]).astype('float32')
next_obs_batch = np.array([next_obs]).astype('float32')
done_batch = np.array([float(done)]).astype('float32')
batch_data = obs_batch,action_batch,reward_batch,next_obs_batch,done_batch
yield batch_data,sum(batch_reward_true)
batch_reward_true.clear()
if self.stage =='train':
next_action = self.agent.sample(next_obs) # 训练阶段使用探索策略
else:
next_action = self.agent.predict(next_obs) # 验证阶段使用模型预测结果
action = next_action
obs = next_obs
if done:
if self.stage=='train' and len(self.rpm)<MEMORY_WARMUP_SIZE: #确保训练一次
yield self.rpm.sample(len(self.rpm)),sum(batch_reward_true)
batch_reward_true.clear()
break
else:
break
def __len__(self):
return self.size
env = gym.make('CartPole-v1')
rpm = ReplayMemory(MEMORY_SIZE)
ds_train = MyDataset(env,agent,rpm,stage='train',size=1000)
ds_val = MyDataset(env,agent,rpm,stage='val',size=200)#ReplayMemory预存数据
while len(ds_train.rpm)<MEMORY_WARMUP_SIZE:
for data in ds_train:
print(len(ds_train.rpm))13
47
167
272
511
521def collate_fn(batch):
samples,rewards = [x[0] for x in batch],[x[-1] for x in batch]
samples = [torch.from_numpy(np.concatenate([x[j] for x in samples])) for j in range(5)]
rewards = torch.from_numpy(np.array([sum(rewards)]).astype('float32'))
return samples,rewards
dl_train = DataLoader(ds_train,batch_size=1,collate_fn=collate_fn)
dl_val = DataLoader(ds_val,batch_size=1,collate_fn=collate_fn)for batch in dl_train:
breakimport sys,datetime
from tqdm import tqdm
import numpy as np
from accelerate import Accelerator
from torchkeras import KerasModel
import pandas as pd
from copy import deepcopy
class StepRunner:
def __init__(self, net, loss_fn, accelerator=None, stage = "train", metrics_dict = None,
optimizer = None, lr_scheduler = None
):
self.net,self.loss_fn,self.metrics_dict,self.stage = net,loss_fn,metrics_dict,stage
self.optimizer,self.lr_scheduler = optimizer,lr_scheduler
self.accelerator = accelerator if accelerator is not None else Accelerator()
def __call__(self, batch):
samples,reward = batch
#torch_data = ([torch.from_numpy(x) for x in batch_data])
loss = self.net.compute_loss(*samples)
#backward()
if self.optimizer is not None and self.stage=="train":
self.accelerator.backward(loss)
if self.accelerator.sync_gradients:
self.accelerator.clip_grad_norm_(self.net.parameters(), 1.0)
self.optimizer.step()
if self.lr_scheduler is not None:
self.lr_scheduler.step()
self.optimizer.zero_grad()
#losses （or plain metric）
step_losses = {self.stage+'_reward':reward.item(),
self.stage+'_loss':loss.item()}
#metrics (stateful metric)
step_metrics = {}
if self.stage=="train":
if self.optimizer is not None:
step_metrics['lr'] = self.optimizer.state_dict()['param_groups'][0]['lr']
else:
step_metrics['lr'] = 0.0
return step_losses,step_metrics
class EpochRunner:
def __init__(self,steprunner,quiet=False):
self.steprunner = steprunner
self.stage = steprunner.stage
self.accelerator = steprunner.accelerator
self.net = steprunner.net
self.quiet = quiet
def __call__(self,dataloader):
dataloader.agent = self.net
n = dataloader.size if hasattr(dataloader,'size') else len(dataloader)
loop = tqdm(enumerate(dataloader,start=1),
total=n,
file=sys.stdout,
disable=not self.accelerator.is_local_main_process or self.quiet,
ncols=100
)
epoch_losses = {}
for step, batch in loop:
if step<n:
step_losses,step_metrics = self.steprunner(batch)
step_log = dict(step_losses,**step_metrics)
for k,v in step_losses.items():
epoch_losses[k] = epoch_losses.get(k,0.0)+v
loop.set_postfix(**step_log)
else:
break
epoch_metrics = step_metrics
epoch_metrics.update({self.stage+"_"+name:metric_fn.compute().item()
for name,metric_fn in self.steprunner.metrics_dict.items()})
epoch_losses = {k:v for k,v in epoch_losses.items()}
epoch_log = dict(epoch_losses,**epoch_metrics)
loop.set_postfix(**epoch_log)
for name,metric_fn in self.steprunner.metrics_dict.items():
metric_fn.reset()
return epoch_log
KerasModel.StepRunner = StepRunner
KerasModel.EpochRunner = EpochRunnerkeras_model = KerasModel(net= agent,loss_fn=None,
optimizer=torch.optim.Adam(agent.model.parameters(),lr=1e-2))
dfhistory = keras_model.fit(train_data = dl_train,
val_data=dl_val,
epochs=600,
ckpt_path='checkpoint.pt',
patience=100,
monitor='val_reward',
mode='max',
callbacks=None,
plot= True,
cpu=True)
四，评估Agent
# 评估 agent, 跑 3 次，总reward求平均
def evaluate(env, agent, render=False):
eval_reward = []
for i in range(2):
obs,info = env.reset()
episode_reward = 0
step=0
while step<300:
action = agent.predict(obs) # 预测动作，只选最优动作
obs, reward, done, _, _ = env.step(action)
episode_reward += reward
if render:
show_state(env,step,info='reward='+str(episode_reward))
if done:
break
step+=1
eval_reward.append(episode_reward)
return np.mean(eval_reward)#直观显示动画
env = gym.make('CartPole-v1',render_mode="rgb_array")
evaluate(env, agent, render=True)
可以看到，训练完成之后，我们的agent已经变得非常的智能了，能够维持倒立摆的平衡超过200s。🤗
288.5
五，保存Agent
torch.save(agent.state_dict(),'dqn_agent.pt')万水千山总是情，点个在看行不行？🤗🤗
本文notebook源码，以及更多有趣范例，可在公众号算法美食屋后台回复关键词：torchkeras，获取~
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