Calculate second-order derivatives.

[iago-lito]

I am mostly interested in candle for its powerful autograd feature and its applications in scientific computing.

But reading from #1241, it appears that using the autograd to access intermediate gradients or calculate second-order derivatives are considered "very hacky things".

Reading from the code, I also learn that second-order derivatives are "out of scope at the moment".

Why exactly is it out of scope and/or considered hacky ?

Is it possible to use candle-core to calculate second-order derivatives at all ?
If yes, how to do so ?