Initial parameters in NUTS that cannot be changed

[AstroParrotKing]

By chance, is it still possible to pass in a custom dense mass matrix?

I see this post but I’m not sure if this works in the latest version.

Post:

Initial mass matrix

Yes: see https://github.com/pymc-devs/pymc3/blob/a3fcc861ae0f160111afb95a574540272de644a3/pymc3/sampling.py#L1511-L1513 and https://github.com/pymc-devs/pymc3/blob/a3fcc861ae0f160111afb95a574540272de644a3/pymc3/sampling.py#L1518 Basically, you need to initialized NUTS by hand using step = pm.NUTS(...), and then pass step to pm.sample(...)