Dear all, How can I see mathematical formulation of variogram models in gstat? Some of them are in gstat manual but there aren't others like ("Exc,"Ste","Mat","Hol"). Thanks. -- Saman Monfared Msc, Department of Statistics, Shiraz University, Shiraz 71454, Iran Email: Samanmonfared1 at gmail.com Tel: +98 917 5305167