[R-sig-ME] GNLS Crash

[Viechtbauer Wolfgang (STAT)]

Hi all,

I'm trying to fit a marginal (longitudinal) model with an exponential serial correlation function to the Orange tree data set. However, R crashes frequently when using the gnls() function. With the following simple example, I was able to reproduce the problem. 

gnls.exp <- gnls(circumference ~ Asym/(1 + exp(-(age-xmid)/scal)) ,
              data = Orange, correlation = corExp(form = ~1 | Tree),
              start = c(Asym=150, xmid=750, scal=300))

On my and one other computer, R usually crashes when calling the gnls() function with this code three times in a row. I stumbled across this when trying to fit this model with different starting values.

Version information:

platform       i386-pc-mingw32             
arch           i386                        
os             mingw32                     
system         i386, mingw32               
status                                     
major          2                           
minor          7.2                         
year           2008                        
month          08                          
day            25                          
svn rev        46428                       
language       R                           
version.string R version 2.7.2 (2008-08-25)

Can anybody help figure out what causes this problem?

Best,

-- 
Wolfgang Viechtbauer 
 Department of Methodology and Statistics 
 University of Maastricht, The Netherlands 
 http://www.wvbauer.com/