Feature request: vectorized finite difference evaluation

[mattsignorelli]

I have an implicit function that is extremely expensive to evaluate. However, it is fully GPU parallelized, in that if a matrix is provided, then each row is evaluated in parallel. For this particular function, the output is a matrix of size = (something, number of rows)

Doing finite differences through this is then easily parallelizable by making each row be a finite difference "tangent" (sorry if I'm misusing that word), so that the full Jacobian can be constructed in one single function evaluation as opposed to many evaluations.

I am doing this now manually, but it would be nice if this functionality could be generalized into FiniteDiff. perhaps a dims argument could be provided to AutoFiniteDiff specifying the dimension about which the evaluation is vectorized (in my case across the rows, so dims=1).