[R] nls model singular gradient matrix parametrization

[Mihai Nica]

Greetings,
I am having a very hard time with a nonlinear regression. The last chance is 
that maybe somebody can spot something wrong… The data and the model are 
described below:

number of observations = 3030
y = [0,…,~16]
D1969 = [.16,…,~70,000]

>mod=nls(log(D1969)~d-log(1+d1*exp(-gt+g1*y)), start=list(d=11, d1=750000, 
>gt=14, g1=.9), trace=TRUE, data=pidg)
Error in nlsModel(formula, mf, start) : singular gradient matrix at initial 
parameter estimates

I ran several variants, changing the start values. However the graph with 
these starting values is almost identical with what is obtained with the 
real data (although it is rather nonlinear)… I am missing something, but 
can’t figure out what. If anybody has a little time and patience, any advice 
would be really really appreciated.
Thanks,


Mihai Nica, ABD
Jackson State University
ITT Tech Instructor
170 East Griffith Street G5
Jackson, MS 39201
601 914 0361

The least of learning is done in the classrooms.
  - Thomas Merton