Selective Parameter Sharing

Official implementation of the ICML 2021 paper Scaling Multi-Agent Reinforcement Learning with Selective Parameter Sharing

Requirements

To run this repository you need: i) To install the code's requirements. A virtual environment is recommended. Install with

pip install -r requirements.txt

ii) Install at least one of the supported environments:

• Multi-Robot Warehouse found here (SePS requires the color branch of RWARE which supports multiple agent types)
• Blind-Particle Spread from our fork of Petting-Zoo here
• Level-Based Foraging found here (Important! LBF must be modified to make agent levels persist across environment resets)
• Starcraft Multi-Agent Challenge here (Careful! Requires installation of SC2 which is a large package. For our implementation you must remove that SMACCompatible wrapper from the configuration, by removing the respective line in ac.py:config)

Running

You can then simply run ac.py using:

    python ac.py with env_name='robotic_warehouse:rware-2color-tiny-4ag-v1' time_limit=500

The above command will load and run the tiny variation of the RWARE task with four agents. Other exciting environments shown in the paper include 'rware-2color-tiny4-ag-hard-v1', 'rware-2color-small-8ag-v1' or 'rware-2color-medium-16ag-v1' (replace in "robotic_warehouse:XXXX" above). Episode time limit should be kept at 500 as above.

The blind particle spread (BPS) environment can be run using:

    python ac.py with env_name='pettingzoo:pz-mpe-large-spread-v1' time_limit=50

In the paper, we have used an episode time limit of 50. v1-v6 contain different scenarios (number of agents/landmarks etc) as described in the paper.

Similarly, LBF and SMAC can be run as long as they are registered in gym.

A note on the hyperparameters

This repository is an implementation of SePS and not necessarily the identical code that generated the experiments (i.e. small bug-fixes, features, or improved hyperparameters will be contained in this repository). Any major bug fixes (if necessary) will be documented below.

Right now, the proposed hyperparameters can be found in the config function of ops_utils.py (for the SePS procedure) and for ac.py (A2C hyperparameters). For SePS (ops_utils.py):

• pretraining_steps: always returns stabler results when increased. Usually works with as low as 2,000, but should be increased to 10,000 if time/memory allows. Simpler environments (like BPS) can handle much smaller values.
• clusters: the number of clusters (K in the paper). Please see respective section in the paper. When # of clusters is unknown Davies–Bouldin index is recommended (scikit-learn function here works well). DB-Index will be used automatically if clusters=None.
• z_features: Typical values of ~5-10 work well with the tested number of types. If this value is set to 2 then a visualisation will be saved at "clusters.png"
• kl_weight: Values near zero work well since it tends to overwhelm the reconstruction loss. Try setting to zero when debugging.
• reconstruct: Could be changed from ["next_obs", "rew"] to only ["next_obs"] or ["rew"] if it known that the environment only changes the observation or reward function respectively (and not both).
• delay/delay_training/pretraining_times: can be used in situation when differences between types are shown later in the training.

In ac.py:

• "algorithm_mode": Can be set to "ops", "iac", "snac-a", "snac-b". These values correspond to "SePS", "NoPS", "FuPS", "FuPS+id" respectively.

model.py

model.py contains a fast implementation of selective parameter sharing for multi-agent RL. It can be used independently from the SePS codebase.
MultiAgentFCNetwork defines a torch network with K independent networks. By passing a list (size>K) of inputs and a laac_index that maps the index of the input to the index of the independent network, it will quickly resolve them and return the desired returns. Example: if a K of 2 is selected and you have four agents, you can pass a laac_index of [0, 0, 1, 1] to share parameters between the first two agents and the last two agents.

Cite:

@inproceedings{christianos2021scaling,
   title={Scaling Multi-Agent Reinforcement Learning with Selective Parameter Sharing},
   author={Filippos Christianos and Georgios Papoudakis and Arrasy Rahman and Stefano V. Albrecht},
   booktitle={International Conference on Machine Learning (ICML)},
   year={2021}
}