lambert C++

LambertW ======== C++ implementation of the Lambert W(x) function. The implementation grew out of the code that was first used in the mathematical utilities of the [Offline Reconstruction Software Framework](http://arxiv.org/abs/0707.1652) of the [Pierre Auger Observatory](http://www.auger.org). The work is described in the following publications: * [arXiv:1003.1628](http://arxiv.org/abs/1003.1628) * [arXiv:1209.0735](http://arxiv.org/abs/1209.0735) and [Comp. Phys. Comm. **183** (2012) 2622-2628](http://dx.doi.org/10.1016/j.cpc.2012.07.008) This is currently the fastest known implementation of the Lambert W function on the planet. ## License Released under dual licence: the GPL version 2 and the two-clause BSD license. Scientific or technical publications resulting from projects using this code are required to add the [Comp. Phys. Comm. **183** (2012) 2622-2628](http://dx.doi.org/10.1016/j.cpc.2012.07.008) citation among their references. ## Usage All the relevant code is placed into an `utl` namespace. The two branches (0 and -1) of the Lambert function can be specified as template parameters, e.g. ```C++ const double w = utl::LambertW<-1>(x); ``` or as normal parameters ```C++ const double w = utl::LambertW(-1, x); ```