Allow keeping the base pose when a model is reduced

[diegoferigo]

No description provided.

[flferretti]

I've tried with my humanoid class for PPO and I've encountered a problem related to the new ABA version in the following line:

jaxsim/src/jaxsim/physics/algos/aba.py

Line 98 in 0eab286

vJ = S[i] * qd[ii]

In fact respect to the one presented in #35 I've seen that you've removed a part of the code:

98c81
< vJ = S[i] * qd[i - 1] if qd.size != 0 else S[i] * 0 
#35
---
> vJ = S[i] * qd[ii]
#42

This should allow to treat the case in which the model has no joints, e.g. in the case of this PR, when every joint is blocked

[diegoferigo]

Thanks, I didn't test this case. Should be fixed now, let me know if you still have problems.

[flferretti]

Thanks for your changes Diego! I'm now encoutering a small issue that I described in #37. In particular, after having reduced the model, when I try to simulate using step_over_horizon the attribute VelRepr is changed to be a DeviceArray. As I said in #37 (comment), making velocity_representation static in the JaxSim class solved the issue for me

[diegoferigo]

Thanks for your changes Diego! I'm now encoutering a small issue that I described in #37. In particular, after having reduced the model, when I try to simulate using step_over_horizon the attribute VelRepr is changed to be a DeviceArray. As I said in #37 (comment), making velocity_representation static in the JaxSim class solved the issue for me

Mmh, I guess that by JIT-compiling a JaxSim class, jax wants to treat the enum of the velocity representation as a parameter that can be changed without triggering recompilation.

This is not something we want to achieve in the short term since it would involve using jax.lax.select everywhere in high_level.model.Model. Since it's already static in Model, I guess it makes sense to keep it as static also in the simulator.

[flferretti]

Thank you for your feedback! Looks good to me