[R] nls, convergence and starting values

[Christian Ritz]

Hi Patrick,

there exist specialized functionality in R that offer both automated calculation of
starting values and relatively robust optimization, which can be used with success in many
common cases of nonlinear regression, also for your data:

library(drc)  # on CRAN

## Fitting 3-parameter logistic model
## (slightly different parameterization from SSlogis())
bdd.m1 <- drm(pourcma~transat, weights=sqrt(nbfeces), data=bdd, fct=L.3())

plot(bdd.m1, broken=TRUE, conLevel=0.0001)

summary(bdd.m1)


Of course, standard errors are huge as the data do not really support this model (as
already pointed out by other replies to this post).


Christian