Example for custom param and gradient types

[Novakasa]

I am currently trying to implement a simple SteepestDescent solver with a custom param type, to facilitate making the gradient calculation in my application smarter. I currently have a hard time satisfying the compiler regarding various missing implementations involving the argmin_math traits.

It would be nice to have an example that involves a custom param (and maybe gradient type) to make it easier for custom implementations. If it already exists, it would be nice if someone can point me to it, and this issue can be closed.