https://github.com/cran/fields
Tip revision: e6e2dec9c9cc857b2226614aaf6c6642000af53c authored by Doug Nychka on 06 February 2009, 00:00:00 UTC
version 5.02
version 5.02
Tip revision: e6e2dec
Exponential.Rd
% 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
\name{Exponential, Matern, Radial Basis}
\alias{Exponential}
\alias{Matern}
\alias{RadialBasis}
\title{Covariance functions}
\description{
Functional form of covariance function assuming the argument is a
distance between locations.
}
\usage{
Exponential(d, range = 1, alpha = 1/range, phi = 1)
Matern (d , scale = 1, range = 1,alpha=1/range,
smoothness = 0.5, nu= smoothness, phi=scale)
RadialBasis(d,M,dimension)
}
%- maybe also 'usage' for other objects documented here.
\arguments{
\item{d}{ Vector of distances }
\item{range}{ Range parameter default is one. Note
that the scale can also be specified through the "theta"
scaling argument used in fields covariance functions) }
\item{alpha}{1/range }
\item{scale}{Same as phi }
\item{phi}{ Marginal variance.}
\item{smoothness}{ Smoothness parameter in Matern. Controls the number
of derivatives in the process. Default is 1/2 corresponding to an exponential
covariance.}
\item{nu}{ Same as smoothness}
\item{M}{Interpreted as a spline M is the order of the derivatives in the
penalty.}
\item{dimension}{Dimension of function}
}
\details{
Exponential:
phi* exp( -d/range)
Matern:
phi*con*(d\^nu) * besselK(d , nu )
Matern covariance function transcribed from Stein's book page 31
nu==smoothness, alpha == 1/range
GeoR parameters map to kappa==smoothness and phi == range
check for negative distances
\code{con} is a constant that normalizes the expression to be 1.0 when phi=1.0
and d=0.
Radial basis functions:
C.m,d d\^(2m-dim) dim- odd
C.m,d d\^(2m-dim)ln( d) dim-even
where C.m.d is a constant based on spline theory. See \code{radbas.constant}.
}
\value{
A vector of covariances.
}
\references{ Stein's book}
\author{Doug Nychka}
\seealso{stationary.cov, stationary.image.cov, Wendland,stationary.taper.cov
rad.cov}
\keyword{spatial}% at least one, from doc/KEYWORDS