https://github.com/cran/fields
Tip revision: 6a574ee78277f7f38ae7939a12894c1616dc61eb authored by Douglas Nychka on 16 October 2015, 01:28:36 UTC
version 8.3-5
version 8.3-5
Tip revision: 6a574ee
cubic.cov.R
# fields, Tools for spatial data
# Copyright 2004-2013, Institute for Mathematics Applied Geosciences
# University Corporation for Atmospheric Research
# Licensed under the GPL -- www.gpl.org/licenses/gpl.html
cubic.cov <- function(x1, x2=NULL, theta = 1, C = NA, marginal = FALSE) {
# comments in Exp.simple.cov for more details about the
# required parts of this covariance
if (is.matrix(x1)) {
if (ncol(x1) != 1) {
stop(" x is a matrix this is a 1-d covariance")
}
}
if( is.null( x2) ){
x2<- x1
}
# local function
fun.temp <- function(u, v) {
1 + ifelse(u < v, v * (u^2)/2 - (u^3)/6, u * (v^2)/2 -
(v^3)/6)
}
if (is.na(C[1]) & !marginal) {
# cross covariance matrix
return(outer(c(x1), c(x2), FUN = fun.temp))
}
if (!is.na(C[1])) {
# product of cross covariance with a vector
return(outer(c(x1), c(x2), FUN = fun.temp) %*% C)
}
if (marginal) {
# marginal variance
return((x1^3)/3)
}
}