Given a sample of size n of positive exceedances, compute
the real shape parameter \(\xi\) based on the k largest order statistics.
shape.pickands(xdat, k)a data frame with the number of order statistics k and the shape parameter estimate shape, or a single numeric value if k is a scalar.
vector of positive observations of length \(n\)
number of largest order statistics
Pickands, III, J. (1975). Statistical inference using extreme order statistics. Annals of Statistics, 3, 119-131.