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#
# fields is a package for analysis of spatial data written for
# the R software environment.
# Copyright (C) 2024 Colorado School of Mines
# 1500 Illinois St., Golden, CO 80401
# Contact: Douglas Nychka, douglasnychka@gmail.com,
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with the R software environment if not, write to the Free Software
# Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
# or see http://www.r-project.org/Licenses/GPL-2
##END HEADER
cubic.cov <- function(x1, x2=NULL, aRange = 1, C = NA, marginal = FALSE,
theta=NULL) {
# comments in Exp.simple.cov for more details about the
# required parts of this covariance
# theta argument has been deopreciated.
if( !is.null( theta)){
aRange<- theta
}
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)
}
}
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