\Header{expcov}{Spatial Covariance Functions}
\alias{gaucov}{expcov}
\alias{sphercov}{expcov}
\keyword{spatial}{expcov}
\begin{Description}\relax
Spatial covariance functions for use with \code{surf.gls}.\end{Description}
\begin{Usage}
\begin{verbatim}
expcov(r, d, alpha=0, se=1)
gaucov(r, d, alpha=0, se=1)
sphercov(r, d, alpha=0, se=1, D=2)
\end{verbatim}
\end{Usage}
\begin{Arguments}
\begin{ldescription}
\item[\code{r}] vector of distances at which to evaluate the covariance

\item[\code{d}] range parameter

\item[\code{alpha}] proportion of nugget effect

\item[\code{se}] standard deviation at distance zero

\item[\code{D}] dimension of spheres.

\end{ldescription}
\end{Arguments}
\begin{Value}
vector of covariance values.\end{Value}
\begin{SeeAlso}\relax
\code{\Link{surf.gls}}\end{SeeAlso}
\begin{Examples}
\begin{ExampleCode}
data(topo)
topo.kr <- surf.ls(2, topo)
correlogram(topo.kr, 25)
d <- seq(0, 7, 0.1)
lines(d, expcov(d, 0.7))
\end{ExampleCode}
\end{Examples}

