Deep Q-Learning (DQN)

Overview

As an extension of the Q-learning, DQN's main technical contribution is the use of replay buffer and target network, both of which would help improve the stability of the algorithm.

Original papers:

• Human-level control through deep reinforcement learning

Implemented Variants

Variants Implemented	Description
dqn.py, docs	For classic control tasks like CartPole-v1.
dqn_atari.py, docs	For playing Atari games. It uses convolutional layers and common atari-based pre-processing techniques.

Below are our single-file implementations of DQN:

dqn.py

The dqn.py has the following features:

• Works with the Box observation space of low-level features
• Works with the Discrete action space
• Works with envs like CartPole-v1

Implementation details

dqn.py includes the 11 core implementation details:

dqn_atari.py

The dqn_atari.py has the following features:

• For playing Atari games. It uses convolutional layers and common atari-based pre-processing techniques.
• Works with the Atari's pixel Box observation space of shape (210, 160, 3)
• Works with the Discrete action space

Usage

poetry install -E atari
python cleanrl/dqn_atari.py --env-id BreakoutNoFrameskip-v4
python cleanrl/dqn_atari.py --env-id PongNoFrameskip-v4

Implementation details

dqn_atari.py is based on (Mnih et al., 2015)¹ but presents a few implementation differences:

1. dqn_atari.py use slightly different hyperparameters. Specifically,
   • dqn_atari.py uses the more popular Adam Optimizer with the --learning-rate=1e-4 as follows:

     optim.Adam(q_network.parameters(), lr=1e-4)
     

     whereas (Mnih et al., 2015)¹ (Exntended Data Table 1) uses the RMSProp optimizer with --learning-rate=2.5e-4, gradient momentum 0.95, squared gradient momentum 0.95, and min squared gradient 0.01 as follows:

     optim.RMSprop(
         q_network.parameters(),
         lr=2.5e-4,
         momentum=0.95,
         # ... PyTorch's RMSprop does not directly support
         # squared gradient momentum and min squared gradient
         # so we are not sure what to put here.
     )
     

   • dqn_atari.py uses --learning-starts=80000 whereas (Mnih et al., 2015)¹ (Exntended Data Table 1) uses --learning-starts=50000.
   • dqn_atari.py uses --target-network-frequency=1000 whereas (Mnih et al., 2015)¹ (Exntended Data Table 1) uses --learning-starts=10000.
   • dqn_atari.py uses --total-timesteps=10000000 (i.e., 10M timesteps = 40M frames because of frame-skipping) whereas (Mnih et al., 2015)¹ uses --total-timesteps=50000000 (i.e., 50M timesteps = 200M frames) (See "Training details" under "METHODS" on page 6 and the related source code run_gpu#L32, dqn/train_agent.lua#L81-L82, and dqn/train_agent.lua#L165-L169).
   • dqn_atari.py uses --end-e=0.01 (the final exploration epsilon) whereas (Mnih et al., 2015)¹ (Exntended Data Table 1) uses --end-e=0.1.
   • dqn_atari.py uses --exploration-fraction=0.1 whereas (Mnih et al., 2015)¹ (Exntended Data Table 1) uses --exploration-fraction=0.02 (all corresponds to 250000 steps or 1M frames being the frame that epsilon is annealed to --end-e=0.1 ).
   • dqn_atari.py treats termination and truncation the same way due to the gym interface² whereas (Mnih et al., 2015)¹ correctly handles truncation.
2. dqn_atari.py use a self-contained evaluation scheme: dqn_atari.py reports the episodic returns obtained throughout training, whereas (Mnih et al., 2015)¹ is trained with --end-e=0.1 but reported episodic returns using a separate evaluation process with --end-e=0.01 (See "Evaluation procedure" under "METHODS" on page 6).
3. dqn_atari.py rescales the gradient so that the norm of the parameters does not exceed 0.5 like done in PPO ( ppo2/model.py#L102-L108).

Experiment results

PR vwxyzjn/cleanrl#124 tracks our effort to conduct experiments, and the reprodudction instructions can be found at vwxyzjn/cleanrl/benchmark/dqn.

Below are the average episodic returns for dqn_atari.py.

Environment	dqn_atari.py 10M steps	(Mnih et al., 2015)1 50M steps
BreakoutNoFrameskip-v4	337.64 ± 69.47	401.2 ± 26.9
PongNoFrameskip-v4	20.293 ± 0.37	18.9 ± 1.3
BeamRiderNoFrameskip-v4	6207.41 ± 1019.96	6846 ± 1619

Learning curves:

Tracked experiments and game play videos:

---

1. Mnih, V., Kavukcuoglu, K., Silver, D. et al. Human-level control through deep reinforcement learning. Nature 518, 529–533 (2015). https://doi.org/10.1038/nature14236 ↩↩↩↩↩↩↩↩↩↩

2. [Proposal] Formal API handling of truncation vs termination. https://github.com/openai/gym/issues/2510 ↩