[R] nls.control()

[Dieter Menne]

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