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agent.py
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import os
import torch
import torch.nn.functional as F
from torch.optim import Adam
from utils import soft_update, hard_update
from model import GaussianPolicy, QNetwork
class SAC(object):
def __init__(self, num_inputs, action_space):
self.gamma = 0.99
self.tau = 0.005
self.alpha = 0.05
self.lr = 0.0005
self.target_update_interval = 1
self.automatic_entropy_tuning = True
self.device = torch.device("cuda:0" if torch.cuda.is_available else "cpu")
self.critic = QNetwork(num_inputs, action_space.shape[0]).to(device=self.device)
self.critic_optim = Adam(self.critic.parameters(), lr=self.lr)
self.critic_target = QNetwork(num_inputs, action_space.shape[0]).to(self.device)
hard_update(self.critic_target, self.critic)
# Target Entropy = −dim(A) (e.g. , -6 for HalfCheetah-v2) as given in the paper
if self.automatic_entropy_tuning is True:
self.target_entropy = -torch.prod(torch.Tensor(action_space.shape).to(self.device)).item()
self.log_alpha = torch.zeros(1, requires_grad=True, device=self.device)
self.alpha_optim = Adam([self.log_alpha], lr=self.lr)
self.policy = GaussianPolicy(num_inputs, action_space.shape[0], action_space).to(self.device)
self.policy_optim = Adam(self.policy.parameters(), lr=self.lr)
def select_action(self, state, evaluate=False):
state = torch.FloatTensor(state).to(self.device).unsqueeze(0)
if evaluate is False:
action, _, _ = self.policy.sample(state)
else:
_, _, action = self.policy.sample(state)
return action.detach().cpu().numpy()[0]
def update_parameters(self, memory, batch_size, updates):
# Sample a batch from memory
state_batch, action_batch, reward_batch, next_state_batch, mask_batch = memory.sample(batch_size=batch_size)
state_batch = torch.FloatTensor(state_batch).to(self.device)
next_state_batch = torch.FloatTensor(next_state_batch).to(self.device)
action_batch = torch.FloatTensor(action_batch).to(self.device)
reward_batch = torch.FloatTensor(reward_batch).to(self.device).unsqueeze(1)
mask_batch = torch.FloatTensor(mask_batch).to(self.device).unsqueeze(1)
with torch.no_grad():
next_state_action, next_state_log_pi, _ = self.policy.sample(next_state_batch)
qf1_next_target, qf2_next_target = self.critic_target(next_state_batch, next_state_action)
min_qf_next_target = torch.min(qf1_next_target, qf2_next_target) - self.alpha * next_state_log_pi
next_q_value = reward_batch + mask_batch * self.gamma * (min_qf_next_target)
qf1, qf2 = self.critic(state_batch, action_batch) # Two Q-functions to mitigate positive bias in the policy improvement step
qf1_loss = F.mse_loss(qf1, next_q_value) # JQ = 𝔼(st,at)~D[0.5(Q1(st,at) - r(st,at) - γ(𝔼st+1~p[V(st+1)]))^2]
qf2_loss = F.mse_loss(qf2, next_q_value) # JQ = 𝔼(st,at)~D[0.5(Q1(st,at) - r(st,at) - γ(𝔼st+1~p[V(st+1)]))^2]
qf_loss = qf1_loss + qf2_loss
self.critic_optim.zero_grad()
qf_loss.backward()
self.critic_optim.step()
pi, log_pi, _ = self.policy.sample(state_batch)
qf1_pi, qf2_pi = self.critic(state_batch, pi)
min_qf_pi = torch.min(qf1_pi, qf2_pi)
policy_loss = ((self.alpha * log_pi) - min_qf_pi).mean() # Jπ = 𝔼st∼D,εt∼N[α * logπ(f(εt;st)|st) − Q(st,f(εt;st))]
self.policy_optim.zero_grad()
policy_loss.backward()
self.policy_optim.step()
if self.automatic_entropy_tuning:
alpha_loss = -(self.log_alpha * (log_pi + self.target_entropy).detach()).mean()
self.alpha_optim.zero_grad()
alpha_loss.backward()
self.alpha_optim.step()
self.alpha = self.log_alpha.exp()
alpha_tlogs = self.alpha.clone() # For TensorboardX logs
else:
alpha_loss = torch.tensor(0.).to(self.device)
alpha_tlogs = torch.tensor(self.alpha) # For TensorboardX logs
if updates % self.target_update_interval == 0:
soft_update(self.critic_target, self.critic, self.tau)
return qf1_loss.item(), qf2_loss.item(), policy_loss.item(), alpha_loss.item(), alpha_tlogs.item()
# Save model parameters
def save_checkpoint(self, env_name, suffix="", ckpt_path=None):
if not os.path.exists('checkpoints/'):
os.makedirs('checkpoints/')
if ckpt_path is None:
ckpt_path = "checkpoints/sac_checkpoint_{}_{}".format(env_name, suffix)
print('Saving models to {}'.format(ckpt_path))
torch.save({'policy_state_dict': self.policy.state_dict(),
'critic_state_dict': self.critic.state_dict(),
'critic_target_state_dict': self.critic_target.state_dict(),
'critic_optimizer_state_dict': self.critic_optim.state_dict(),
'policy_optimizer_state_dict': self.policy_optim.state_dict()}, ckpt_path)
# Load model parameters
def load_checkpoint(self, ckpt_path, evaluate=False):
print('Loading models from {}'.format(ckpt_path))
if ckpt_path is not None:
checkpoint = torch.load(ckpt_path)
self.policy.load_state_dict(checkpoint['policy_state_dict'])
self.critic.load_state_dict(checkpoint['critic_state_dict'])
self.critic_target.load_state_dict(checkpoint['critic_target_state_dict'])
self.critic_optim.load_state_dict(checkpoint['critic_optimizer_state_dict'])
self.policy_optim.load_state_dict(checkpoint['policy_optimizer_state_dict'])
if evaluate:
self.policy.eval()
self.critic.eval()
self.critic_target.eval()
else:
self.policy.train()
self.critic.train()
self.critic_target.train()