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Update README on integrators and contact models #375

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Update README on integrators and contact models #375

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11 changes: 4 additions & 7 deletions README.md
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Expand Up @@ -332,19 +332,16 @@ The algorithms and some simulation features were inspired by its accompanying [c

The development of JaxSim started in late 2021, inspired by early versions of [`google/brax`][brax].
At that time, Brax was implemented in maximal coordinates, and we wanted a physics engine in reduced coordinates.
We are grateful to the Brax team for their work and showing the potential of [JAX][jax] in this field.
We are grateful to the Brax team for their work and for showing the potential of [JAX][jax] in this field.

Brax v2 was later implemented reduced coordinates, following an approach comparable to JaxSim.
The development then shifted to [MJX][mjx], which today provides a JAX-based implementation of the Mujoco APIs.
Brax v2 was later implemented with reduced coordinates, following an approach comparable to JaxSim.
The development then shifted to [MJX][mjx], which provides a JAX-based implementation of the Mujoco APIs.

The main differences between MJX/Brax and JaxSim are as follows:

- JaxSim supports out-of-the-box all SDF models with [Pose Frame Semantics][PFS].
- JaxSim only supports collisions between points rigidly attached to bodies and a compliant ground surface.
Our contact model requires careful tuning of its spring-damper parameters, but being an instantaneous
function of the state $(\mathbf{q}, \boldsymbol{\nu})$, it doesn't require running any optimization algorithm
when stepping the simulation forward.
- JaxSim mitigates the stiffness of the contact-aware system dynamics by providing variable-step integrators.
- JaxSim experimentally supports variable-step integrators to mitigate the stiffness of the contact-aware system dynamics.
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Did we re-introduce somewhere the variable step integator ? By looking at the other related PR I did not find it. Maybe we can directly remove this line for now


[brax]: https://github.com/google/brax
[mjx]: https://mujoco.readthedocs.io/en/3.0.0/mjx.html
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