Hello,
I have some questions regarding the roboschool HalfCheetah.

I see that the observation space for HalfCheetah is 26. Can anyone tell me what is each value for  I counted 18? (also, some of the values seem to remain 0 for all timesteps)

In the half_cheetah.xml under roboschool/mujoco_assets, there is the following comment:
Cheetah Model
The state space is populated with joints in the order that they are
defined in this file. The actuators also operate on joints.
StateSpace (name/joint/parameter):
 rootx slider position (m)
 rootz slider position (m)
 rooty hinge angle (rad)
 bthigh hinge angle (rad)
 bshin hinge angle (rad)
 bfoot hinge angle (rad)
 fthigh hinge angle (rad)
 fshin hinge angle (rad)
 ffoot hinge angle (rad)
 rootx slider velocity (m/s)
 rootz slider velocity (m/s)
 rooty hinge angular velocity (rad/s)
 bthigh hinge angular velocity (rad/s)
 bshin hinge angular velocity (rad/s)
 bfoot hinge angular velocity (rad/s)
 fthigh hinge angular velocity (rad/s)
 fshin hinge angular velocity (rad/s)
 ffoot hinge angular velocity (rad/s)
Could you please confirm to me if the order presented here is the same with the order they appear in the observation matrix?
Thank you.