Log Message:
math/R-numDeriv: Import version 2016.8.1

Methods for calculating (usually) accurate numerical first and second
order derivatives. Accurate calculations are done using 'Richardson”s'
extrapolation or, when applicable, a complex step derivative is
available. A simple difference method is also provided. Simple
difference is (usually) less accurate but is much quicker than
'Richardson”s' extrapolation and provides a useful cross-check.
Methods are provided for real scalar and vector valued functions.