What is ard_num_dims useful for?

What is ard_num_dims useful for? Are there any use cases for when you’d want ARD for some kernel parameters but not others (at least within the context of a single constructor call)?. It’s also not clear what the expected behavior is when ard_num_dims is not equal to the number of dimensions being fed into the kernel.

[Balandat]

Sounds reasonable to me. I can put up a PR for that if @gpleiss and @jacobrgardner are ok with that soft deprecation.

[eytan]

If this is something you wanted to change, I would recommend introducing new kwargs / phasing out the old API incrementally (e.g., introduce input_dims and an ard flag kwargs, and throw a warning that they should be more explicit, and then later take the old API away in one or two point releases). Personally, I find it to be a lot less magical and intuitive as a new user. Perhaps y’all will want to see if the ard continues to be a point of confusion, and if it does, come up with some plan to slowly move people to some required input dimension w/ a boolean flag for ARD.