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Exponential.R
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Exponential.R
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# fields is a package for analysis of spatial data written for
# the R software environment .
# Copyright (C) 2018
# University Corporation for Atmospheric Research (UCAR)
# Contact: Douglas Nychka, nychka@ucar.edu,
# National Center for Atmospheric Research, PO Box 3000, Boulder, CO 80307-3000
#
# 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
"Exponential" <- function(d, range = 1, alpha = 1/range, phi = 1.0,
theta=NULL) {
#
# 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
# to make old code from Fuentes and also the package SEHmodel
# phi is accepted as the marginal variance of the process (see below)
# within fields this parameter is "sigma"
#
# check for negative distances
# theta argument has been depreciated.
if( !is.null( theta)){
aRange<- theta
}
if (any(d < 0))
stop("distance argument must be nonnegative")
#
return(phi*exp(-d * alpha))
}