[Rd] extracting and manipulating components from nlme and gnls objects

[Nicholas Lewin-Koh]

Hello,
I am writing a set of functions to do prediction and calibration
intervals 
for at least the subset of selfstarting models if not some more general
ones.

I need to be able to extract the varFunction from a fit object
and evaluate it at a predicted point. Are there any examples around?

Also in a self start model, say SSlogis, how would I get the gradient
at a point?

Thanks
Nicholas

PS I am sure I will have more questions