Soft Actor-Critic (SAC) is an off-policy Actor-Critic algorithm for continuous action space. In SAC, it introduces an entropy regularization to the loss function, which has a close connection with the trade-off of the exploration and exploitation. In our implementation, we employ a learnable entropy regularization coefficienct to dynamic control the scale of the entropy, which makes it consistent with a pre-defined target entropy. SAC also utilizes Clipped Double-Q Learning (mentioned in TD3) to overcome the overestimation of Q-values. This implementation provides SAC and supports the following extensions:

  • Experience replay: ✔️

  • Target network: ✔️

  • Gradient clipping: ✔️

  • Reward clipping: ❌

  • Prioritized Experience Replay (PER): ✔️

  • Leanable entropy regularization coefficient: ✔️


Inspired by the delayed policy update from TD3, we implement a modified version of SAC AgentModSAC with a dynamic adjustment of the frequency of the policy update. The adjustment is based on the loss of critic networks: a small loss leads to a high update frequency and vise versa.

Code Snippet

import torch
from import train_and_evaluate
from elegantrl.config import Arguments
from elegantrl.train.config import build_env
from elegantrl.agents.AgentSAC import AgentSAC

# train and save
args = Arguments(env=build_env('Pendulum-v0'), agent=AgentSAC())
args.cwd = 'demo_Pendulum_SAC'
args.env.target_return = -200
args.reward_scale = 2 ** -2

# test
agent = AgentSAC()
agent.init(args.net_dim, args.state_dim, args.action_dim)
agent.save_or_load_agent(cwd=args.cwd, if_save=False)

env = build_env('Pendulum-v0')
state = env.reset()
episode_reward = 0
for i in range(2 ** 10):
    action = agent.select_action(state)
    next_state, reward, done, _ = env.step(action)

    episode_reward += reward
    if done:
        print(f'Step {i:>6}, Episode return {episode_reward:8.3f}')
        state = next_state


class elegantrl.agents.AgentSAC.AgentSAC(net_dim: int, state_dim: int, action_dim: int, gpu_id: int = 0, args=None)[source]
class elegantrl.agents.AgentSAC.AgentModSAC(net_dim, state_dim, action_dim, gpu_id=0, args=None)[source]

Bases: AgentSAC

Modified SAC with introducing of reliable_lambda, to realize “Delayed” Policy Updates.

  • net_dim[int] – the dimension of networks (the width of neural networks)

  • state_dim[int] – the dimension of state (the number of state vector)

  • action_dim[int] – the dimension of action (the number of discrete action)

  • learning_rate[float] – learning rate of optimizer

  • if_per_or_gae[bool] – PER (off-policy) or GAE (on-policy) for sparse reward

  • env_num[int] – the env number of VectorEnv. env_num == 1 means don’t use VectorEnv

  • agent_id[int] – if the visible_gpu is ‘1,9,3,4’, agent_id=1 means (1,9,4,3)[agent_id] == 9


Update the neural networks by sampling batch data from ReplayBuffer.

  • buffer – the ReplayBuffer instance that stores the trajectories.

  • batch_size – the size of batch data for Stochastic Gradient Descent (SGD).

  • repeat_times – the re-using times of each trajectory.

  • soft_update_tau – the soft update parameter.


a tuple of the log information.


class*args: Any, **kwargs: Any)[source]
class*args: Any, **kwargs: Any)[source]