How to get a linearized model from mujoco

[bolorkhuu]

My setup

mujoco: 3.3.0, ubuntu

My question

Hello,
i have a simple system model in xml, i would like to calculate the A, B state space model matrix from the mujoco model linearized at a certain equilibrium point. is there a easy way get them? thank you. i got the B matrix first column from the inverted mass matrix, but getting the A matrix seems not easy.

[v-r-a]

Hi, I am a MujoCo user, hope this helps:

Please check the function mjd_transitionFD to obtain A and B matrices using numerical finite differencing. I prefer to use the centered differences, flg_centered = True. You need to set the equilibrium point by setting d.qpos and d.qvel. You can find a use case in the LQR tutorial here.

You may find earlier issues and discussions useful. Search with keywords: state transition matrix or mjd_transition.

[bolorkhuu]

thank you. it works, btw its outputs seem discrete A, B matrices, that i can convert into continues time

A = logm(A) / dt
B = B / dt

which are slightly different than from the analytical calculated continues A, B matrices, is there any mujoco function to calculate continues time A, B matrices?

[v-r-a]

Nope...