R help - Jan 2008 - nlme model specification (revisit)

Hi List,

While using 'nlme' function, I have encountered the similar problem Dr.
Stevens and Dr. Graves observed (please see the posts:
https://stat.ethz.ch/pipermail/r-help/2006-May/105832.html ).  I have tried Dr.
Stevens's original example, the problem is still there,

> mod.lis <- nlsList(circumference ~  SSlogis(age, Asymp, xmid, scal),
+              data=Orange )
> 
> mod <- nlme(circumference ~  SSlogis(age, Asymp, xmid, scal),
+              data=Orange,
+              fixed = Asymp + xmid + scal ~ 1,
+              start = fixef(mod.lis) )
> 
> mod <- nlme(circumference ~  SSlogis(age, Asymp, xmid, scal),
+              data=Orange,
+              fixed = list(Asymp ~ 1, xmid ~ 1, scal ~ 1),
+              start = fixef(mod.lis) )
Error in parse(file, n, text, prompt, srcfile, encoding) : 
        syntax error, unexpected END_OF_INPUT in "~
"
> sessionInfo()
R version 2.5.1 (2007-06-27) 
i386-pc-mingw32 

locale:
LC_COLLATE=English_United States.1252;LC_CTYPE=English_United
States.1252;LC_MONETARY=English_United
States.1252;LC_NUMERIC=C;LC_TIME=English_United States.1252

attached base packages:
[1] "stats"     "graphics"  "grDevices"
"utils"     "datasets"  "methods"  
"base"

other attached packages:
  lattice      nlme 
"0.15-11"  "3.1-86" 


Just wondering if you guys have any answers for this since I didn't see any
for the original posts.

Thanks,

...Tao
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