Can `MjModel.jnt_dofadr` be used for accessing `MjData.qacc`?

[adlarkin]

Hello, I'm new to MuJoCo and I'm trying to test a simple two-link arm hitting a sphere in a zero gravity environment. I am recording the positions, velocities, and accelerations of the bodies after each simulation step so that I can plot this data.

The floating objects section of the documentation shows how to get the joint addresses for qpos and qvel. Is the address returned by MjModel.jnt_dofadr a valid address for accessing the joint's acceleration via MjData.qacc, or can this address only be used to access MjData.qvel? My intuition tells me that jnt_dofadr should work for both qvel and qacc (i.e., the dimensionality of the velocity and acceleration should be the same), but the documentation and code comments for jnt_dofadr indicate that this should only be used for qvel. Also, the fact that this field is called jnt_dofadr instead of something like jnt_qveladr makes me think that it's applicable to both qvel and qacc.

Here's the model I'm using:

simple_arm_zero_gravity.xml

```XML ```

Additional details: OS: Ubuntu 22.04 Python version: 3.10.12 MuJoCo version: 3.1.3 (installed in a venv with the Python version listed above)

[Balint-H]

Hello,

Your assumptions are correct, qvel and qacc are aligned, the same index refers to the same DoF on the model (unlike qpos). So you can use dofadr for both!

[adlarkin]

Awesome, thanks for confirming!