varFixed {nlme} | R Documentation |
This function is a constructor for the varFixed
class,
representing a variance function with fixed variances. Letting v
denote the variance covariate defined in value
, the variance
function s2(v) for this class is
s2(v)=|v|. The variance covariate v is
evaluated once at initialization and remains fixed thereafter. No
coefficients are required to represent this variance function.
varFixed(value)
value |
a one-sided formula of the form |
a varFixed
object representing a fixed variance function
structure, also inheriting from class varFunc
.
JosÃ© Pinheiro and Douglas Bates bates@stat.wisc.edu
Pinheiro, J.C., and Bates, D.M. (2000) "Mixed-Effects Models in S and S-PLUS", Springer.
varClasses
,
varWeights.varFunc
,
varFunc
vf1 <- varFixed(~age)