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Hyperparameter Tuning

CleanRL comes with a simple and practical hyperparameter tuning utility Tuner.

Get started

Create the following file:

tuner_example.py
from cleanrl_utils.tuner import Tuner
tuner = Tuner(
    script="cleanrl/ppo.py",
    metric="charts/episodic_return",
    metric_last_n_average_window=50,
    direction="maximize",
    target_scores={
        "CartPole-v1": [0, 500],
    },
    params_fn=lambda trial: {
        "learning-rate": trial.suggest_loguniform("learning-rate", 0.0003, 0.003),
        "num-minibatches": trial.suggest_categorical("num-minibatches", [1, 2, 4]),
        "update-epochs": trial.suggest_categorical("update-epochs", [1, 2, 4]),
        "num-steps": trial.suggest_categorical("num-steps", [5, 16, 32, 64, 128]),
        "vf-coef": trial.suggest_uniform("vf-coef", 0, 5),
        "max-grad-norm": trial.suggest_uniform("max-grad-norm", 0, 5),
        "total-timesteps": 10000,
        "num-envs": 4,
    },
)
tuner.tune(
    num_trials=100,
    num_seeds=3,
)

Then you can run the tuner with 

poetry install optuna
python tuner_example.py

Here is what happened:

  1. The tuner_example.py launches num_trials=100 trials to find the best single set of hyperparameters for CartPole-v1 in script="cleanrl/ppo.py".
  2. Each trial uses a set of hyperparameters sampled from the params_fn to run num_seeds=3 experiments with different random seeds, mitigating the impact of randomness on the results.
    • In each experiment, tuner_example.py averages the last metric_last_n_average_window=50 reported metric="charts/episodic_return" to a number \(x_i\) and calculate a normalized score \(z_i = (x_i - 0) / (500 - 0)\) according to target_scores, where \(0\) and \(500\) are the minimum and maximum values of the metric for CartPole-v1.
  3. Each trial then averages the normalized scores \(z_i\) of the three experiments to a number \(z\) and the tuner optimizes \(z\) according direction="maximize".

Visualization

Running python tuner_example.py will create a sqlite database containing all of the hyperparameter trials in ./cleanrl_hpopt.db. We can use optuna-dashboard to visualize the process.

poetry run optuna-dashboard sqlite:///cleanrl_hpopt.db

You can use a different database by passing Tuner(..., storage="mysql://root@localhost/example"), for example.

Work w/ multiple environments

Tuner supports finding a set of hyper parameters of that works well against multiple environments by extending target_scores. In the following example, each trial uses a set of hyperparameters to run experiments with 3 random seeds for each environment in ["CartPole-v1","Acrobot-v1"], totalling 2*3=6 experiments per trial.

tuner_example_multi_env.py
from cleanrl_utils.tuner import Tuner
tuner = Tuner(
    script="cleanrl/ppo.py",
    metric="charts/episodic_return",
    metric_last_n_average_window=50,
    direction="maximize",
    target_scores={
        "CartPole-v1": [0, 500],
        "Acrobot-v1": [-500, 0],
    },
    params_fn=lambda trial: {
        "learning-rate": trial.suggest_loguniform("learning-rate", 0.0003, 0.003),
        "num-minibatches": trial.suggest_categorical("num-minibatches", [1, 2, 4]),
        "update-epochs": trial.suggest_categorical("update-epochs", [1, 2, 4]),
        "num-steps": trial.suggest_categorical("num-steps", [5, 16, 32, 64, 128]),
        "vf-coef": trial.suggest_uniform("vf-coef", 0, 5),
        "max-grad-norm": trial.suggest_uniform("max-grad-norm", 0, 5),
        "total-timesteps": 10000,
        "num-envs": 16,
    },
)
tuner.tune(
    num_trials=100,
    num_seeds=3,
)
Info

When optimizing Atari games, you can use target_scores as the human normalized scores in (Mnih et al., 2015, Extended Data Table 2)1, such as 

tuner = Tuner(
    script="cleanrl/ppo_atari.py",
    metric="charts/episodic_return",
    metric_last_n_average_window=50,
    direction="maximize",
    target_scores={
        "Alien-v5": [227.8, 6875],
        "Amidar-v5": [5.8, 1676],
        'Assault-v5': (222.4, 1496),
        'Asterix-v5': (210.0, 8503),
        'Asteroids-v5': (719.1, 13157),
        ...
    },
    ...
)

Work w/ pruners

You can use Tuner with any pruner from optuna to prune less promising experiments:

tuner_example_pruner.py
import optuna
from cleanrl_utils.tuner import Tuner
tuner = Tuner(
    script="cleanrl/ppo.py",
    metric="charts/episodic_return",
    metric_last_n_average_window=50,
    direction="maximize",
    target_scores={
        "CartPole-v1": [0, 500],
        "Acrobot-v1": [-500, 0],
    },
    params_fn=lambda trial: {
        "learning-rate": trial.suggest_loguniform("learning-rate", 0.0003, 0.003),
        "num-minibatches": trial.suggest_categorical("num-minibatches", [1, 2, 4]),
        "update-epochs": trial.suggest_categorical("update-epochs", [1, 2, 4]),
        "num-steps": trial.suggest_categorical("num-steps", [5, 16, 32, 64, 128]),
        "vf-coef": trial.suggest_uniform("vf-coef", 0, 5),
        "max-grad-norm": trial.suggest_uniform("max-grad-norm", 0, 5),
        "total-timesteps": 10000,
        "num-envs": 16,
    },
    pruner=optuna.pruners.MedianPruner(n_startup_trials=5),
)
tuner.tune(
    num_trials=100,
    num_seeds=3,
)

Track experiments w/ Weights and Biases

The Tuner can track all the experiments into Weights and Biases to help you visualize the progress of the tuning.

tuner_example.py
import optuna
from cleanrl_utils.tuner import Tuner
tuner = Tuner(
    script="cleanrl/ppo.py",
    metric="charts/episodic_return",
    metric_last_n_average_window=50,
    direction="maximize",
    target_scores={
        "CartPole-v1": [0, 500],
        "Acrobot-v1": [-500, 0],
    },
    params_fn=lambda trial: {
        "learning-rate": trial.suggest_loguniform("learning-rate", 0.0003, 0.003),
        "num-minibatches": trial.suggest_categorical("num-minibatches", [1, 2, 4]),
        "update-epochs": trial.suggest_categorical("update-epochs", [1, 2, 4]),
        "num-steps": trial.suggest_categorical("num-steps", [5, 16, 32, 64, 128]),
        "vf-coef": trial.suggest_uniform("vf-coef", 0, 5),
        "max-grad-norm": trial.suggest_uniform("max-grad-norm", 0, 5),
        "total-timesteps": 10000,
        "num-envs": 16,
    },
    pruner=optuna.pruners.MedianPruner(n_startup_trials=5),
    wandb_kwargs={"project": "cleanrl"},
)
tuner.tune(
    num_trials=100,
    num_seeds=3,
)

  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 ↩