import torch
import numpy as np
from copy import deepcopy
from torch.distributions import Independent, Normal
from typing import Any, Dict, Tuple, Union, Optional
from tianshou.policy import DDPGPolicy
from tianshou.exploration import BaseNoise
from tianshou.data import Batch, ReplayBuffer, to_torch_as
[docs]class SACPolicy(DDPGPolicy):
"""Implementation of Soft Actor-Critic. arXiv:1812.05905.
:param torch.nn.Module actor: the actor network following the rules in
:class:`~tianshou.policy.BasePolicy`. (s -> logits)
:param torch.optim.Optimizer actor_optim: the optimizer for actor network.
:param torch.nn.Module critic1: the first critic network. (s, a -> Q(s,
a))
:param torch.optim.Optimizer critic1_optim: the optimizer for the first
critic network.
:param torch.nn.Module critic2: the second critic network. (s, a -> Q(s,
a))
:param torch.optim.Optimizer critic2_optim: the optimizer for the second
critic network.
:param action_range: the action range (minimum, maximum).
:type action_range: Tuple[float, float]
:param float tau: param for soft update of the target network, defaults to
0.005.
:param float gamma: discount factor, in [0, 1], defaults to 0.99.
:param (float, torch.Tensor, torch.optim.Optimizer) or float alpha: entropy
regularization coefficient, default to 0.2.
If a tuple (target_entropy, log_alpha, alpha_optim) is provided, then
alpha is automatatically tuned.
:param bool reward_normalization: normalize the reward to Normal(0, 1),
defaults to False.
:param bool ignore_done: ignore the done flag while training the policy,
defaults to False.
:param BaseNoise exploration_noise: add a noise to action for exploration,
defaults to None. This is useful when solving hard-exploration problem.
:param bool deterministic_eval: whether to use deterministic action (mean
of Gaussian policy) instead of stochastic action sampled by the policy,
defaults to True.
.. seealso::
Please refer to :class:`~tianshou.policy.BasePolicy` for more detailed
explanation.
"""
def __init__(
self,
actor: torch.nn.Module,
actor_optim: torch.optim.Optimizer,
critic1: torch.nn.Module,
critic1_optim: torch.optim.Optimizer,
critic2: torch.nn.Module,
critic2_optim: torch.optim.Optimizer,
action_range: Tuple[float, float],
tau: float = 0.005,
gamma: float = 0.99,
alpha: Union[
float, Tuple[float, torch.Tensor, torch.optim.Optimizer]
] = 0.2,
reward_normalization: bool = False,
ignore_done: bool = False,
estimation_step: int = 1,
exploration_noise: Optional[BaseNoise] = None,
deterministic_eval: bool = True,
**kwargs: Any,
) -> None:
super().__init__(None, None, None, None, action_range, tau, gamma,
exploration_noise, reward_normalization, ignore_done,
estimation_step, **kwargs)
self.actor, self.actor_optim = actor, actor_optim
self.critic1, self.critic1_old = critic1, deepcopy(critic1)
self.critic1_old.eval()
self.critic1_optim = critic1_optim
self.critic2, self.critic2_old = critic2, deepcopy(critic2)
self.critic2_old.eval()
self.critic2_optim = critic2_optim
self._is_auto_alpha = False
self._alpha: Union[float, torch.Tensor]
if isinstance(alpha, tuple):
self._is_auto_alpha = True
self._target_entropy, self._log_alpha, self._alpha_optim = alpha
assert alpha[1].shape == torch.Size([1]) and alpha[1].requires_grad
self._alpha = self._log_alpha.detach().exp()
else:
self._alpha = alpha
self._deterministic_eval = deterministic_eval
self.__eps = np.finfo(np.float32).eps.item()
[docs] def train(self, mode: bool = True) -> "SACPolicy":
self.training = mode
self.actor.train(mode)
self.critic1.train(mode)
self.critic2.train(mode)
return self
[docs] def sync_weight(self) -> None:
for o, n in zip(
self.critic1_old.parameters(), self.critic1.parameters()
):
o.data.copy_(o.data * (1.0 - self._tau) + n.data * self._tau)
for o, n in zip(
self.critic2_old.parameters(), self.critic2.parameters()
):
o.data.copy_(o.data * (1.0 - self._tau) + n.data * self._tau)
[docs] def forward( # type: ignore
self,
batch: Batch,
state: Optional[Union[dict, Batch, np.ndarray]] = None,
input: str = "obs",
**kwargs: Any,
) -> Batch:
obs = batch[input]
logits, h = self.actor(obs, state=state, info=batch.info)
assert isinstance(logits, tuple)
dist = Independent(Normal(*logits), 1)
if self._deterministic_eval and not self.training:
x = logits[0]
else:
x = dist.rsample()
y = torch.tanh(x)
act = y * self._action_scale + self._action_bias
y = self._action_scale * (1 - y.pow(2)) + self.__eps
log_prob = dist.log_prob(x).unsqueeze(-1)
log_prob = log_prob - torch.log(y).sum(-1, keepdim=True)
if self._noise is not None and self.training and not self.updating:
act += to_torch_as(self._noise(act.shape), act)
act = act.clamp(self._range[0], self._range[1])
return Batch(
logits=logits, act=act, state=h, dist=dist, log_prob=log_prob)
def _target_q(
self, buffer: ReplayBuffer, indice: np.ndarray
) -> torch.Tensor:
batch = buffer[indice] # batch.obs: s_{t+n}
with torch.no_grad():
obs_next_result = self(batch, input='obs_next')
a_ = obs_next_result.act
target_q = torch.min(
self.critic1_old(batch.obs_next, a_),
self.critic2_old(batch.obs_next, a_),
) - self._alpha * obs_next_result.log_prob
return target_q
[docs] def learn(self, batch: Batch, **kwargs: Any) -> Dict[str, float]:
weight = batch.pop("weight", 1.0)
# critic 1
current_q1 = self.critic1(batch.obs, batch.act).flatten()
target_q = batch.returns.flatten()
td1 = current_q1 - target_q
critic1_loss = (td1.pow(2) * weight).mean()
# critic1_loss = F.mse_loss(current_q1, target_q)
self.critic1_optim.zero_grad()
critic1_loss.backward()
self.critic1_optim.step()
# critic 2
current_q2 = self.critic2(batch.obs, batch.act).flatten()
td2 = current_q2 - target_q
critic2_loss = (td2.pow(2) * weight).mean()
# critic2_loss = F.mse_loss(current_q2, target_q)
self.critic2_optim.zero_grad()
critic2_loss.backward()
self.critic2_optim.step()
batch.weight = (td1 + td2) / 2.0 # prio-buffer
# actor
obs_result = self(batch)
a = obs_result.act
current_q1a = self.critic1(batch.obs, a).flatten()
current_q2a = self.critic2(batch.obs, a).flatten()
actor_loss = (self._alpha * obs_result.log_prob.flatten()
- torch.min(current_q1a, current_q2a)).mean()
self.actor_optim.zero_grad()
actor_loss.backward()
self.actor_optim.step()
if self._is_auto_alpha:
log_prob = obs_result.log_prob.detach() + self._target_entropy
alpha_loss = -(self._log_alpha * log_prob).mean()
self._alpha_optim.zero_grad()
alpha_loss.backward()
self._alpha_optim.step()
self._alpha = self._log_alpha.detach().exp()
self.sync_weight()
result = {
"loss/actor": actor_loss.item(),
"loss/critic1": critic1_loss.item(),
"loss/critic2": critic2_loss.item(),
}
if self._is_auto_alpha:
result["loss/alpha"] = alpha_loss.item()
result["alpha"] = self._alpha.item() # type: ignore
return result