Original version created on: Aug 14, 2013 Authors: L.
Moneta, J. T. Offermann Modified version created on: Sep 27, 2017 Author: E. G. P. Bos
NumericalDerivator was essentially a slightly modified copy of code written by M. Winkler, F. James, L. Moneta, and A. Zsenei for Minuit2, Copyright (c) 2005 LCG ROOT Math team, CERN/PH-SFT. Original version: https://github.com/lmoneta/root/blob/lvmini/math/mathcore/src/NumericalDerivator.cxx
This class attempts to more closely follow the Minuit2 implementation. Modified things (w.r.t. original) are indicated by MODIFIED.