One place for random seed

[jacobpennington]

Pick a single location for a default random seed (probably in nems/__init__.py) and a simple scheme for setting it automatically at runtime (i.e. either set it in init, or at the top of modules that make use of it if that's not sufficient).

[jacobpennington]

Alternatively, jax describes a different rng system based on branching a single process. That sounds more like what we want, but I would need to see if it (or something similar) can be used independently.