https://github.com/cran/fields
Tip revision: 6c8b30169bba182a68765ee3cb9b4e2ef7d38332 authored by Doug Nychka on 16 November 2011, 00:00:00 UTC
version 6.6.3
version 6.6.3
Tip revision: 6c8b301
exp.cov.r
# fields, Tools for spatial data
# Copyright 2004-2011, Institute for Mathematics Applied Geosciences
# University Corporation for Atmospheric Research
# Licensed under the GPL -- www.gpl.org/licenses/gpl.html
"Exp.cov" <- function(x1, x2, theta = rep(1, ncol(x1)),
p = 1, C = NA, marginal = FALSE) {
if (!is.matrix(x1))
x1 <- as.matrix(x1)
if (missing(x2))
x2 <- x1
if (!is.matrix(x2))
x2 <- as.matrix(x2)
if (length(theta) == 1)
theta <- rep(theta, ncol(x1))
d <- ncol(x1)
n1 <- nrow(x1)
n2 <- nrow(x2)
# scale the coordinates by theta
# a more general scaling by a matrix is done in stationary.cov
x1 <- scale(x1, center = FALSE, scale = theta)
x2 <- scale(x2, center = FALSE, scale = theta)
par <- p
#
# there are three possible actions listed below:
# find cross covariance matrix
if (is.na(C[1]) & !marginal) {
return(exp(-rdist(x1, x2)^p))
}
#
# multiply cross covariance matrix by C
# in this case implemented in FORTRAN
#
if (!is.na(C[1])) {
return(.Fortran("multeb", nd = as.integer(d), x1 = as.double(x1),
n1 = as.integer(n1), x2 = as.double(x2), n2 = as.integer(n2),
par = as.double(par), c = as.double(C), h = as.double(rep(0,
n1)), work = as.double(rep(0, n2)))$h)
}
#
# return marginal variance ( 1.0 in this case)
if (marginal) {
return(rep(1, nrow(x1)))
}
}