Recently, in various research projects, the Lambert-W function arose a number of times. Somewhat frustratingly, there is no built-in function in R to calculate it. The only options were those in the gsl and LambertW packages, the latter merely importing the former. Importing the entire GNU Scientific Library (GSL) can be a bit of a hassle, especially for those of us restricted to a Windows environment.

Therefore, I spent a little time and built a package for R whose sole purpose is to calculate the real-valued versions of the Lambert W function without the need for importing the GSL: the lamW package. It does depends on Rcpp, though. It could have been written in pure R, but as there are a number of loops involved which cannot be vectorized, and as Rcpp is fast becoming almost a base package, I figured that the speed and convenience was worth it.

A welcome outcome of this was that I think I finally wrapped my head around basic Padé approximation, which I use when calculating some parts of the primary branch of the Lambert-W. Eventually, I’d like to write a longer post about Padé approximation; when that will happen, who knows 8-).