Going through the R-Dev list, I have found this (from Pedro Afalo),
dated 8 April 2004:
Dear Richard,
The problem that you report is documented (but no solution given) in the
file ch08.R in the scripts directory of nlme package.
I have found the following workaround just by chance, but it
Dear listers,
I am trying to fit a nlme model with age and pds as reals, and
zone a factor with two levels Annaba and Boumalek . The best
model found is the following:
modm3
Nonlinear mixed-effects model fit by maximum likelihood
Model: pds ~ Asym/(1 + exp((xmid - age)/scal))
Data:
