>> 
>> 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

I adjusted the nls() statement by adding the algorithm="port" statement.  Without changing the 
confint(vonB) request or including a lower/upper statement (I'm still not sure what they do), 
I was given

         2.5%     97.5%
Linf 462.8386        NA
k          NA 0.6944959
t0         NA 0.7973458

It's not until I get down to confint(VonB, level=.31) that I get confidence interval values for 
all of the parameter estimates in the model.  Any thoughts or ideas as to why? 


Steven H. Ranney
 
Graduate Research Assistant (Ph.D) 
USGS Montana Cooperative Fishery Research Unit 
Montana State University 
P.O. Box 173460 
Bozeman, MT 59717-3460 

phone: (406) 994-6643 
fax: (406) 994-7479


	[[alternative HTML version deleted]]

