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\name{RMnonstwm}
\alias{RMnonstwm}
\title{Non-stationary Whittle-Matern Covariance Model}
\description{
The non-stationary Whittle-Matern model
\eqn{C} is given by
\deqn{C(x, y)=\Gamma(\mu) \Gamma(\nu(x))^{-1/2} \Gamma(\nu(y))^{-1/2}
W_{\mu} (|x-y|)}{C(x, y)=\Gamma(\mu) \Gamma(\nu(x))^{-1/2}
\Gamma(\nu(y))^{-1/2}
W_{\mu} (|x-y|)}
where \eqn{\mu = [\nu(x) + \nu(y)]/2}, and
\eqn{\nu} must be a positive function.
\eqn{W_{\mu}} is the
covariance of the \command{\link{RMwhittle}} model or the
\command{\link{RMmatern}} model.
}
\details{
The non-stationary Whittle-Matern models are obtained by
the respective stationary model, replacing the
real-valued argument for \code{nu} by a non-negative function.
}
\note{
It cannot be checked whether \code{nu} only takes positive values. So
the responsibility is completely left to the user.
}
\references{
\itemize{
\item Stein, M. (2005)
Nonstationary Spatial Covariance Functions.
Tech. Rep., 2005
}
}
\me
\seealso{
\command{\link{RMwhittle}},
\command{\link{RMmodel}},
\command{\link{RFsimulate}},
\command{\link{RFfit}}.
}
\examples{\dontshow{StartExample()}
RFoptions(seed=0) ## *ANY* simulation will have the random seed 0; set
## RFoptions(seed=NA) to make them all random again
x <- seq(-1.2, 1.2, len=50)
model <- RMwhittle(nu=RMgauss())
%plot(model, dim=2, xlim=c(-1,1))
z <- RFsimulate(model=model, x, x, n=4)
plot(z)
\dontshow{FinalizeExample()}}
\keyword{spatial}
\keyword{models}
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