PolyTran's constructor that takes only forward coefficients provides an iterative inverse by default (as does its other constructor if the forward coefficient array is empty). This seems like a bad idea for several reasons:
- Most polynomials do not have unique inverses. That said, the iterative inverse will do sensible things in that situation (nan if no value exists, else a valid value if multiple choices exist).
- The iterative inverse is much less efficient to compute than the fit inverse provided by `PolyMap.polyTran`.
I propose to disable the iterative inverse by default, using the philosophy of "when in doubt, refuse to guess".