corSpher {nlme} | R Documentation |
Spherical Correlation Structure
Description
This function is a constructor for the corSpher
class,
representing a spherical spatial correlation structure. Letting
denote the range and
denote the nugget
effect, the correlation between two observations a distance
apart is
when no
nugget effect is present and
when a nugget effect is assumed. If
the
correlation is zero. Objects created using this constructor must later
be initialized using the appropriate
Initialize
method.
Usage
corSpher(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 corSpher
, also inheriting from class
corSpatial
, representing a spherical 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 <- corSpher(form = ~ x + y)
# example lme(..., corSpher ...)
# 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
fm6BW.lme <- update(fm3BW.lme,
correlation = corSpher(form = ~ Time))
# example gls(..., corSpher ...)
# Pinheiro and Bates, pp. 261, 263
fm1Wheat2 <- gls(yield ~ variety - 1, Wheat2)
# p. 262
fm2Wheat2 <- update(fm1Wheat2, corr =
corSpher(c(28, 0.2),
form = ~ latitude + longitude, nugget = TRUE))