bug: Default Parameter in PoweredExponential

[ChrisBoettner]

Bug Report

GPJax version:

0.8.0

Current behavior:

Hi,
I'm new to GPJax (and Jax) in general, so please excuse me if I'm being naive here, but I think there is some weird behavior in the default parameter of the PoweredExponential kernel. Specifically, the power gets set to 1 by default, with a default sigmoid bijector. This leads to the parameter to be inf, when running model.unconstrain(), which makes the fit fail with no obvious reason.
It's definitely something that can be fixed very easily by setting a different initial value to power, but I doubt this is the intended behaviour.

Best wishes,
Chris