https://github.com/cran/fields
Tip revision: 0e015763c23043fc79b36e20177cde5e8b4eb092 authored by Doug Nychka on 06 July 2010, 19:17:12 UTC
version 6.3
version 6.3
Tip revision: 0e01576
Exponential.R
# fields, Tools for spatial data
# Copyright 2004-2007, Institute for Mathematics Applied Geosciences
# University Corporation for Atmospheric Research
# Licensed under the GPL -- www.gpl.org/licenses/gpl.html
"Exponential" <- function(d, range = 1, alpha = 1/range,
phi = 1) {
#
# Matern covariance function transcribed from Stein's book page 31
# nu==smoothness==.5, alpha == 1/range
#
# GeoR parameters map to kappa==smoothness and phi == range
# check for negative distances
if (any(d < 0))
stop("distance argument must be nonnegative")
#
return(phi * exp(-d * alpha))
}