[R] Variance functions in package nlme

[Thilo Kellermann]

Dear R-help,

I am trying to set up linear mixed effects models in R using the (recommended) 
nlme package (R version 2.3.1 on a Linux platform). When trying to reproduce 
an example from Jose Pinheiro & Douglas Bates (2000, p 210) I get the 
following error message (code to produce message pasted as well):

library("nlme")
data("Orthodont")
vf1Ident <- varIdent( c(Female = 0.5), form = ~ 1 | Sex )
vf1Ident <- initialize(vf1Ident, Orthodont)
Error in getClass(Class) : c("\"varIdent\" is not a defined class", 
"\"varFunc\" is not a defined class")
In addition: Warning message:
the condition has length > 1 and only the first element will be used in: if 
(!is.na(match(Class, .BasicClasses))) return(newBasic(Class,  

Can anybody give me a hint, what's going wrong here?
Thanks a lot,

Thilo

Reference:
Jose C. Pinheiro & Douglas M. Bates (2000) Mixed-Effects Models in S and 
S-PLUS. Springer, New York.

-- 
Thilo Kellermann
Department of Psychiatry and Psychotherapy
RWTH Aachen University
Pauwelstr. 30
52074 Aachen
Tel.: +49 (0)241 / 8089977
Fax.: +49 (0)241 / 8082401
E-Mail: thilo at izkf.rwth-aachen.de