Half Cheetah

This Environment is part of MaMuJoCo environments. Please read that page first for general information. The task is Gymansium’s MuJoCo/Half Cheetah.

Action Space

The shape of the action space depends on the partitioning. The partitioning has the following form:

if partitioning is None:

Instantiate	env = mamujoco_v1.parallel_env("HalfCheetah", None)
Agents	agents= ['agent_0']
Number of Agents	1
Action Spaces	{'agent_0' : Box(-1, 1, (6,), float32)}
Part partition	[(bthigh, bshin, bfoot, fthigh, fshin, ffoot)]

If partitioning, is None, then the environment contains a single agent with the same action space as Gymansium’s MuJoCo/Half_Cheetah.

Num	Action	Control Min	Control Max	Name (in corresponding XML file)	Joint	Unit
0	Torque applied on the back thigh rotor	-1	1	bthigh	hinge	torque (N m)
1	Torque applied on the back shin rotor	-1	1	bshin	hinge	torque (N m)
2	Torque applied on the back foot rotor	-1	1	bfoot	hinge	torque (N m)
3	Torque applied on the front thigh rotor	-1	1	fthigh	hinge	torque (N m)
4	Torque applied on the front shin rotor	-1	1	fshin	hinge	torque (N m)
5	Torque applied on the front foot rotor	-1	1	ffoot	hinge	torque (N m)

if partitioning == “2x3”: # front and back

Instantiate	env = mamujoco_v1.parallel_env("HalfCheetah", "2x3")
Agents	agents= ['agent_0', 'agent_1']
Number of Agents	2
Action Spaces	{'agent_0' : Box(-1, 1, (3,), float32), 'agent_1' : Box(-1, 1, (3,), float32)}
Part partition	[(bthigh, bshin, bfoot), (fthigh, fshin, ffoot)]

The environment is partitioned in 2 parts, the front part (containing the front leg) and the back part (containing the back leg)

Agent 0 action space (front leg)

Num	Action	Control Min	Control Max	Name (in corresponding XML file)	Joint	Unit
0	Torque applied on the back thigh rotor	-1	1	bthigh	hinge	torque (N m)
1	Torque applied on the back shin rotor	-1	1	bshin	hinge	torque (N m)
2	Torque applied on the back foot rotor	-1	1	bfoot	hinge	torque (N m)

Agent 1 action space (back leg)

Num	Action	Control Min	Control Max	Name (in corresponding XML file)	Joint	Unit
0	Torque applied on the front thigh rotor	-1	1	fthigh	hinge	torque (N m)
1	Torque applied on the front shin rotor	-1	1	fshin	hinge	torque (N m)
2	Torque applied on the front foot rotor	-1	1	ffoot	hinge	torque (N m)

if partitioning == “6x1”: # each joint

Instantiate	env = mamujoco_v1.parallel_env("HalfCheetah", "6x1")
Agents	agents= ['agent_0', 'agent_1', 'agent_2', 'agent_3', 'agent_4', 'agent_5']
Number of Agents	6
Action Spaces	{Box(-1, 1, (1,), float32)}
Part partition	[(bthigh,), (bshin,), (bfoot,), (fthigh,), (fshin,), (ffoot,)]

The environment is partitioned in 6 parts, each part corresponding to a single joint

Agent 0 action space

Num	Action	Control Min	Control Max	Name (in corresponding XML file)	Joint	Unit
0	Torque applied on the back thigh rotor	-1	1	bthigh	hinge	torque (N m)

Agent 1 action space

Num	Action	Control Min	Control Max	Name (in corresponding XML file)	Joint	Unit
0	Torque applied on the back shin rotor	-1	1	bshin	hinge	torque (N m)

Agent 2 action space

Num	Action	Control Min	Control Max	Name (in corresponding XML file)	Joint	Unit
0	Torque applied on the back foot rotor	-1	1	bfoot	hinge	torque (N m)

Agent 3 action space

Num	Action	Control Min	Control Max	Name (in corresponding XML file)	Joint	Unit
0	Torque applied on the front thigh rotor	-1	1	fthigh	hinge	torque (N m)

Agent 4 action space

Num	Action	Control Min	Control Max	Name (in corresponding XML file)	Joint	Unit
0	Torque applied on the front shin rotor	-1	1	fshin	hinge	torque (N m)

Agent 5 action space

Num	Action	Control Min	Control Max	Name (in corresponding XML file)	Joint	Unit
0	Torque applied on the front foot rotor	-1	1	ffoot	hinge	torque (N m)

Observation Space

Observation Categories
Default local_categories	[["qpos", "qvel"], ["qpos"]]
Default global_categories	("qpos", "qvel")
Supported observation categories	"qpos", "qvel"

Besides the local observation of each agent (which depend on their parts of the agent, the observation categories and the observation depth), each agent also observes the position and velocity items of the half cheetah’s tip. See more at the Gymnasium’s Half Cheetah.

Rewards

All agents receive the same Gymnasium’s Half Cheetah reward.

Starting state

The starting state of the environment is the same as Gymnasium’s Half Cheetah.

Episode End

All agent terminate and truncate at the same time, given the same conditions as Gymnasium’s Half Cheetah.

Version History

• v1:

  • Now based on Gymnasium/MuJoCo-v5 instead of Gymnasium/MuJoCo-v4 (https://github.com/Farama-Foundation/Gymnasium/pull/572).

• v0: Initial version release, uses Gymnasium.MuJoCo-v4, and is a fork of the original MaMuJoCo schroederdewitt/multiagent_mujoco. Changes from the original MaMuJoCo (schroederdewitt/multiagent_mujoco):

  • Added/Fixed Global observations (The Cheetah’s front tip: rootx, rooty, rootz) not being observed.

  • Changed action ordering to be same as Gymnasium/MuJoCo/HalfCheetah