[R] nls.control()

Dieter Menne
Wed, 03 Sep 2008 06:00:04 -0000

Ranney, Steven <steven.ranney <at> montana.edu> writes:

>
> and I'm trying to fit a simple Von Bertalanffy growth curve with
program:
>
> VonB=nls(TL~Linf*(1-exp(-k*(age-t0))), data=box5.4,
>     start=list(Linf=1000, k=0.1, t0=0.1), trace=TRUE)
...
> Everything works as it should right up until the confint(VonB) statement.
When I ask
> for the confidence intervals, R goes through the process then stops and
gives
>
> "Error in prof$getProfile() :
>   step factor 0.000488281 reduced below 'minFactor' of
0.000976562".
>
> However, when I use nls.control=(minFactor=0.000001) OR
nls.control(minFactor=0.000001),

In my experience, it never helps to reduce the control factors once this error
comes up; it is a problem that by profiling you hit a boundary where
convergence problems are serious.

Suggestions: first, try with some smaller p-value, e.g. 0.8 or 0.7 instead of
the default of 0.95; profiling will stay in safer region.

It may be possible to use algorithm "port" in combination with
lower/upper, but
I am not sure if this is honoured by profile.

Dieter