[R] skip non-converging nls() in a list

[Marc Belisle]

Howdee,

My question appears at #6 below:

1. I want to model the growth of each of a large number of individuals using
a 4-parameter logistic growth curve.

2. nlme does not converge with the random structure that I want to use.

3. nlsList does not converge for some individuals.

4. I decided to go around nlsList using:

t(sapply(split(data, list(data$id)),
    function(subd){coef(nls(mass ~ SSfpl(age, A, B, xmid, scal), data =
subd))}))

5. This does not converge either:

'Error in nls(y ~ cbind(1, 1/(1 + exp((xmid - x)/exp(lscal)))), data = xy,
:
        singular gradient'

6. Would anyone know if I can get R to skip non-converging use of nls() so
that I can at least obtain the parameters for the curves which R can fit?

Thanks for your time,

Marc

===================
Marc Bélisle
Professeur adjoint
Chaire de recherche du Canada en écologie spatiale et en écologie du paysage
Département de biologie
Université de Sherbrooke
2500 Boul. de l'Université
Sherbrooke, Québec
J1K 2R1 Canada

Tél: +1-819-821-8000 poste 61313
Fax: +1-819-821-8049
Courriél: Marc.M.Belisle at USherbrooke.ca