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.
WWW: https://cran.r-project.org/web/packages/numDeriv/
