[R] nlme model specification

[Martin Henry H. Stevens]

Hi folks,
I am tearing my hair out on this one.
I am using an example from Pinheiro and Bates.

### this works
data(Orange)
mod.lis <- nlsList(circumference ~  SSlogis(age, Asymp, xmid, scal),
             data=Orange )

### This works
mod <- nlme(circumference ~  SSlogis(age, Asymp, xmid, scal),
             data=Orange,
             fixed = Asymp + xmid + scal ~ 1,
             start = fixef(mod.lis) )

### I try a slightly different model specification for the fixed  
effects, and it does not work.
###  fixed = list(Asymp ~ 1, xmid ~ 1, scal ~ 1)
### I tried following the example on page 355.

mod <- nlme(circumference ~  SSlogis(age, Asymp, xmid, scal),
             data=Orange,
             fixed = list(Asymp ~ 1, xmid ~ 1, scal ~ 1),
             start = fixef(mod.lis) )
### I get
Error in parse(file, n, text, prompt) : syntax error in "~ "


nlme version 3.1-71

 > version
                _
platform       powerpc-apple-darwin8.6.0
arch           powerpc
os             darwin8.6.0
system         powerpc, darwin8.6.0
status
major          2
minor          3.0
year           2006
month          04
day            24
svn rev        37909
language       R
version.string Version 2.3.0 (2006-04-24)
 >

Dr. M. Hank H. Stevens, Assistant Professor
338 Pearson Hall
Botany Department
Miami University
Oxford, OH 45056

Office: (513) 529-4206
Lab: (513) 529-4262
FAX: (513) 529-4243
http://www.cas.muohio.edu/~stevenmh/
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http://www.muohio.edu/botany/
"E Pluribus Unum"