[R-sig-Geo] gls with fixed nugget

[Suhel Quader]

Hello all,

Does anyone know whether it is possible to specify a fixed nugget in a GLS 
model, while allowing the range to vary in the optimization?

I am using gls() in the nlme package, with exponential correlation 
structure. One can pass (initial) values of the range and nugget to corExp. 
One can also pass an optional logical value to the "fixed" argument, but 
this affects both range and nugget. Is there a way to control their values 
separately?

I'd appreciate any advice!

Many thanks,
  Suhel

Suhel Quader, PhD
Department of Zoology
University of Cambridge