[Gretl-devel] Mann-Kendall test

Hi, I've just read about the non-parametric Mann-Kendall test for a trend (hence my recent postings about Kendall's tau and ties in a series). It looked pretty easy, so I'm attaching an attempt at a basic implementation. Full disclosure: I've used the description from https://cran.r-project.org/web/packages/trend/vignettes/trend.pdf (only the basic version in section 1.1). All you have to do is call "MannKendall(x)", where x is your series of interest. I'd be happy about feedback regarding cross-checks and correctness (for example in the above document in equ. (4) the case S>0 wrongly appears twice, and I had to make an educated guess where to switch the signs...), whether it should become a function package and so on. thanks, sven