Algorithm 743, real W function

We implement W-function approximation scheme described by Barry et al. A range of tests of the approximations is included so that the code can be assessed on any given machine. Users can calculate W(x) by specifying x itself or by specifying an offset from −exp(−1), the latter option necessitated by rounding errors that can arise for x close to −exp(−1). Results of running the code on a SUN workstation are included.