Vector-value differential operators

[pnkraemer]

It would be quite incredible if one could make the finite difference coefficients handle vector-valued functions/operators well. For example, the Jacobian.

One difficulty will be that the number of dimensions could become quite awkward...

[pnkraemer]

I think some good API decision would be to matchthe shapes of input and outputs to what would've been returned by AD (https://jax.readthedocs.io/en/latest/notebooks/autodiff_cookbook.html).

See also https://findiff.readthedocs.io/en/latest/source/examples-vector-calculus.html