Dear list

I am trying to fit a GLS model with a spherical correlation structure. 
The model runs with out producing any error messages. I have scaled the dataframe before running the analysis (using the function scale()), but three of the parameter estimates are between 3000 and 5000. 

In the process of trying to figure out what is going on, I noted that the number of iterations is zero, which I do not quite understand. Looking in the documentation for the glsObject it says:
  "numIter  the number of iterations used in the iterative algorithm"
Should that number not be at least 1 then?

I have noted that other data sets also produces this situation.

Here is an example:

require(nlme)
# Here with an example from the corSpher function
# example gls(..., corSpher ...)
# Pinheiro and Bates, pp. 261, 263
fm1Wheat2 <- gls(yield ~ variety - 1, Wheat2)
# p. 262
fm2Wheat2 <- update(fm1Wheat2, corr = corSpher(c(28, 0.2), form = ~ latitude + longitude, nugget = TRUE))
fm2Wheat2$numIter  # 0

# sessionInfo()
# R version 2.15.2 (2012-10-26)
# Platform: x86_64-apple-darwin9.8.0/x86_64 (64-bit)
# 
# locale:
#   [1] en_GB.UTF-8/en_GB.UTF-8/en_GB.UTF-8/C/en_GB.UTF-8/en_GB.UTF-8
# 
# attached base packages:
#   [1] stats     graphics  grDevices utils     datasets  methods  
# [7] base     
# 
# other attached packages:
#   [1] nlme_3.1-106
# 
# loaded via a namespace (and not attached):
#   [1] grid_2.15.2     lattice_0.20-10 tools_2.15.2   

Thanks in advance

-Lars
Lars Dalby, Msc., PhD student
E: lada@dmu.dk | T: +45 871 59013
Department of Bioscience, Aarhus University
Grenåvej 14, 8410 Rønde, Denmark




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