implicit integrator

[thowell]

add implicit integrator
https://github.com/google-deepmind/mujoco/blob/e1e224892531c01ad2cb3ac3924d4e7362908e88/src/engine/engine_forward.c#L1094

this feature will require implementing mjd_rne_vel
https://github.com/google-deepmind/mujoco/blob/e1e224892531c01ad2cb3ac3924d4e7362908e88/src/engine/engine_derivative.c#L596

[zer-art]

Hi @thowell, I would like to work on this issue. I understand the requirements regarding the implicit integrator and mjd_rne_vel. Could you please assign it to me?

[Arsh123344423]

Hi @thowell Can i also work upon this issue or is it closed?