Brax Version 0.0.11 Release Notes
This version introduces a significant overhaul to the physics algorithms. We now support position based dynamics for resolving joint and collision constraints. See [this paper](https://matthias-research.github.io/pages/publications/PBDBodies.pdf) for details about PBD.
The most noticeable difference to prior versions of Brax is that joints are now modeled as infinitely stiff, whereas before they were stiff damped spring systems. This new physics is now default, and all environments use PBD-based joints and collisions by default.
If you would like to preserve the behavior used in previous versions of brax, you can either:
1. Version pin to `0.0.10` – the version right before this upgrade. While you will not get the latest and greatest improvements to Brax, you will have unambiguously consistent behavior.
2. Add `dynamics_mode: "legacy_spring"` to your brax configuration file. This causes brax to navigate the old codepath.
3. Supply `legacy_spring=True,` as a kwarg to env creation (without `s). This causes Brax to load the older config for all the environments currently defined in Brax (see the logic in the init functions of each env for details).
Thank you for using Brax, and feel free to open an Issue if you have any questions!