corGaus {nlme} | R Documentation |
Gaussian Correlation Structure
Description
This function is a constructor for the corGaus
class,
representing a Gaussian spatial correlation structure. Letting
d
denote the range and n
denote the nugget
effect, the correlation between two observations a distance
r
apart is \exp(-(r/d)^2)
when no nugget
effect is present and (1-n) \exp(-(r/d)^2)
when a nugget effect is assumed. Objects created using this
constructor must later be initialized using the appropriate
' Initialize
method.
Usage
corGaus(value, form, nugget, metric, fixed)
Arguments
value |
an optional vector with the parameter values in
constrained form. If |
form |
a one sided formula of the form |
nugget |
an optional logical value indicating whether a nugget
effect is present. Defaults to |
metric |
an optional character string specifying the distance
metric to be used. The currently available options are
|
fixed |
an optional logical value indicating whether the
coefficients should be allowed to vary in the optimization, or kept
fixed at their initial value. Defaults to |
Value
an object of class corGaus
, also inheriting from class
corSpatial
, representing a Gaussian spatial correlation
structure.
Author(s)
José Pinheiro and Douglas Bates bates@stat.wisc.edu
References
Cressie, N.A.C. (1993), "Statistics for Spatial Data", J. Wiley & Sons.
Venables, W.N. and Ripley, B.D. (2002) "Modern Applied Statistics with S", 4th Edition, Springer-Verlag.
Littel, Milliken, Stroup, and Wolfinger (1996) "SAS Systems for Mixed Models", SAS Institute.
Pinheiro, J.C., and Bates, D.M. (2000) "Mixed-Effects Models in S and S-PLUS", Springer.
See Also
Initialize.corStruct
,
summary.corStruct
,
dist
Examples
sp1 <- corGaus(form = ~ x + y + z)
# example lme(..., corGaus ...)
# Pinheiro and Bates, pp. 222-249
fm1BW.lme <- lme(weight ~ Time * Diet, BodyWeight,
random = ~ Time)
# p. 223
fm2BW.lme <- update(fm1BW.lme, weights = varPower())
# p 246
fm3BW.lme <- update(fm2BW.lme,
correlation = corExp(form = ~ Time))
# p. 249
fm8BW.lme <- update(fm3BW.lme, correlation = corGaus(form = ~ Time))