xpag 0.1.8

xpag: Exploring Agents

xpag ("exploring agents") is a modular reinforcement learning library with JAX agents, currently in beta version.

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Install

Option 1: conda (preferred option)

This option is preferred because it relies mainly on conda-forge packages (which among other things simplifies the installation of JAX).

git clone https://github.com/perrin-isir/xpag.git
cd xpag
conda update conda

Install micromamba if you don't already have it (you can also simply use conda, by replacing below micromamba create, micromamba update and micromamba activate respectively by conda env create, conda env update and conda activate, but this will lead to a significantly slower installation):

conda install -c conda-forge micromamba

Choose an environment name, for instance xpagenv.
The following command creates the xpagenv environment with the requirements listed in environment.yaml:

micromamba create --name xpagenv --file environment.yaml

If you prefer to update an existing environment (existing_env):

micromamba update --name existing_env --file environment.yaml

Then, activate the xpagenv environment:

micromamba activate xpagenv

Finally, install the xpag library in the activated environment:

pip install -e .

Option 2: pip

For the pip install, you need to properly install JAX yourself. Otherwise, if JAX is installed automatically as a pip dependency of xpag, it will probably not work as desired (e.g. it will not be GPU-compatible). So you should install it beforehand, following these guidelines:

https://github.com/google/jax#installation

Then, install xpag with:

pip install xpag

JAX

To verify that the JAX installation went well, check the backend used by JAX with the following command:

python -c "import jax; print(jax.lib.xla_bridge.get_backend().platform)"

It will print "cpu", "gpu" or "tpu" depending on the platform JAX is using.

Tutorials

The following libraries, not required by xpag, are required for the tutorials:

• MuJoCo (pip install mujoco): see https://github.com/deepmind/mujoco
• imageio (pip install imageio): see https://github.com/imageio/imageio

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Tutorials

The xpag-tutorials repository contains a list of tutorials (colab notebooks) for xpag:
https://github.com/perrin-isir/xpag-tutorials

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Short documentation

xpag: a platform for goal-conditioned RL

xpag allows standard reinforcement learning, but it has been designed with goal-conditioned reinforcement learning (GCRL) in mind (check out the train_gmazes.ipynb tutorial for a simple example of GCRL).

In GCRL, agents have a goal, which is part of the input they take, and the reward mainly depends on the degree of achievement of that goal. Beyond the usual modules in RL platforms (environment, agent, buffer/sampler), xpag introduces a module called "setter" which, among other things, can help to set and manage goals (for example modifying the goal several times in a single episode). Although the setter is largely similar to an environment wrapper, it is separated from the environment because in some cases it should be considered as an independent entity (e.g. a teacher), or as a part of the agent itself.

xpag relies on a single reinforcement learning loop (the learn() function in xpag/tools/learn.py) in which the environment, the agent, the buffer and the setter interact (see below). The learn() function has the following first 3 arguments (returned by gym_vec_env() and brax_vec_env()):

• env: the training environment, which runs 1 or more rollouts in parallel.
• eval_env: the evaluation environment, identical to env except that it runs a single rollout.
• env_info: a dictionary containing information about the environment:
  • env_info["env_type"]: the type of environment; for the moment xpag differentiates 3 types of environments: "Brax" environments, "Mujoco" environments, and "Gym" environments. This information is used to adapt the way episodes are saved and replayed.
  • env_info["name"]: the name of the environment.
  • env_info["is_goalenv"]: whether the environment is a goal-based environment or not.
  • env_info["num_envs"]: the number of parallel rollouts in env
  • env_info["max_episode_steps"]: the maximum number of steps in episodes (xpag does not allow potentially infinite episodes).
  • env_info["action_space"]: the action space (of type gym.spaces.Space) that takes into account parallel rollouts. It can be useful to sample random actions.
  • env_info["single_action_space"]: the action space (of type gym.spaces.Space) for single rollouts.

learn() also takes in input the agent, the buffer and the setter and various parameters. Detailed information about the arguments of learn() can be found in the code documentation (check xpag/tools/learn.py).

The components that interact during learning are:

the environment (env)

In xpag, environments must allow parallel rollouts, and xpag keeps the same API even in the case of a single rollout, i.e. when the number of "parallel environments" is 1. Basically, all environments are "vector environments".

• env.reset(seed: Optional[Union[int, List[int]]], options: Optional[dict]) -> observation: Union[np.array, jax.numpy.array], info: dict
  Following the gym Vector API (see https://www.gymlibrary.dev/api/vector/#vectorenv), environments have a reset() function that returns an observation (which is actually a batch of observations for all the parallel rollouts) and an optional dictionary info (see https://www.gymlibrary.dev/api/vector/#reset).
  We expect observation to be a numpy array, or a jax.numpy array, and its first dimension selects between parallel rollouts, which means that observation[i] is the observation in the i-th rollout. In the case of a single rollout, observation[0] is the observation in this rollout.

• env.step(action: Union[np.array, jax.numpy.array]) -> observation, reward, terminated, truncated, info
  Again, following the gym Vector API, environments have a step() function that takes in input an action (which is actually a batch of actions, one per rollout) and returns: observation, reward, terminated, truncated, info (cf. https://www.gymlibrary.dev/api/vector/#step). There are slight differences with the gym Vector API. First, in xpag this API also covers the case of a single rollout. Second, xpag assumes that reward, terminated and truncated have shape (n, 1), not (n,) (where n is the number of parallel rollouts). More broadly, whether they are due to a single rollout or to unidimensional elements, single-dimensional entries are not squeezed in xpag. Third, in xpag, info is a dictionary, not a tuple of dictionaries (however its entries may be tuples).

• env.reset_done(done, seed: Optional[Union[int, List[int]]], options: Optional[dict]) -> observation, info
  The most significant difference with the gym Vector API is that xpag requires a reset_done() function which takes a done array of Booleans in input and performs a reset for the i-th rollout if and only if done[i] is evaluated to True. Besides done, the arguments of reset_done() are the same as the ones of reset(): seed and options, and its outputs are also the same: observation, info. For rollouts that are not reset, the returned observation is the same as the observation returned by the last step(). reset() must be called once for the initial reset, and afterwards only reset_done() should be used. Auto-resets (automatic resets after terminal transitions) are not allowed in xpag. The main reason to prefer reset_done() to auto-resets is that with auto-resets, terminal transitions must be special and contain additional information. With reset_done(), this is no longer necessary. Furthermore, by modifying the done array returned by a step of the environment, it becomes possible to easily force the termination of an episode, or to force an episode to continue despite reaching a terminal transition (but this must be done with caution).

• gym_vec_env(env_name: str, num_envs: int, wrap_function: Callable = None) -> env, eval_env, env_info: dict
brax_vec_env(env_name: str, num_envs: int, wrap_function: Callable = None, *, force_cpu_backend : bool = False) -> env, eval_env, env_info: dict
  The gym_vec_env() and brax_vec_env() functions (see tutorials) call wrappers that automatically add the reset_done() function to Gym and Brax environments, and make the wrapped environments fit the xpag API.

• Goal-based environments:
  Goal-based environments (for GCRL) must have a similar interface to the one defined in the Gym-Robotics library (see GoalEnv in core.py), with minor differences. Their observation spaces are of type gym.spaces.Dict, with the following keys in the observation dictionaries: "observation", "achieved_goal", and "desired_goal". Goal-based environments must also have in attribute a compute_reward() function that computes rewards. In xpag, the inputs of compute_reward() can be different from the ones considered in the original GoalEnv class. For example, in the GoalEnvWrapper class, which can be used to turn standard environments into goal-based environments, the arguments of compute_reward() are assumed to be achieved_goal (the goal achieved after step()), desired_goal (the desired goal before step()), action, observation (the observation after step()), reward (the reward of the base environment), terminated, truncated and info (the outputs of the step() function). In the version of HER (cf. https://arxiv.org/pdf/1707.01495.pdf) in xpag, it is assumed that compute_reward() depends only on achieved_goal, desired_goal, action and observation.
  In goal-based environments, the multiple observations from parallel rollouts are concatenated as in the gym function concatenate() (cf. https://github.com/openai/gym/blob/master/gym/vector/utils/numpy_utils.py), which means that the batched observations are always single dictionaries in which the entries "observation", "achieved_goal" and "desired_goal" are arrays of observations, achieved goals and desired goals.

• info
  xpag assumes that, in goal-based environments, the info dictionary returned by step() always contains info["is_success"], an array of Booleans (one per rollout) that are True if the corresponding transition is a successfull achievement of the desired goal, and False otherwise (remark: this does not need to coincide with episode termination).

the agent (agent)

xpag only considers off-policy agents. (TODO)

the buffer (buffer)

TODO

the sampler (sampler)

TODO

the setter (setter)

TODO

The figure below summarizes the RL loop and the interactions between the components: (TODO)

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Acknowledgements

• Maintainer and main contributor:

  • Nicolas Perrin-Gilbert (CNRS, ISIR)

  Other people who contributed to xpag:

  • Olivier Serris (ISIR)
  • Alexandre Chenu (ISIR)
  • Stéphane Caron (Inria)
  • Fabian Schramm (Inria)

• The SAC agent is based on the implementation of SAC in JAXRL, and some elements of the TQC agent come from the implementation of TQC in RLJAX.

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Citing the project

To cite this repository in publications:

@misc{xpag,
  author = {Perrin-Gilbert, Nicolas},
  title = {xpag: a modular reinforcement learning library with JAX agents},
  year = {2022},
  url = {https://github.com/perrin-isir/xpag}
}