Re: [R] nlme problems

From: Spencer Graves <spencer.graves_at_pdf.com>
Date: Tue 20 Dec 2005 - 03:42:47 EST

          Are you familiar with Pinheiro and Bates (2000) Mixed-Effects Models in S and S-Plus (Springer)? I suspect that book, especially the latter half, might contain the information you seek.

          spencer graves
p.s. PLEASE do read the posting guide! "www.R-project.org/posting-guide.html". Anecdotal evidence suggests that posts more consistent with that guide tend to receive quicker, more useful replies.

Ken Beath wrote:

> I meant fitting not maximising, it is a nonlinear mixed effects
> model, with both fixed and random effects. My assumption is that for
> the function I am using the approximation approach used in nlme is
> not quite close enough, and nothing much that I can do, except for
> looking at starting values. I was hoping that someone would have
> other suggestions, so I will keep attempting to understand the
> control parameters. I can add an extra parameter to the model and
> obtain a worse fit.
>
> Ken
>
> Dieter Menne writes:
>

>>>I'm maximising a reasonably complex function using nlme (version
>>>3.1-65, have also tried 3.1-66) and am having trouble with fixed
>>>parameter estimates slightly away from the maximum of the log
>>>likelihood. I have profiled the log likelihood and it is a parabola
>>>but with sum dips. Interestingly changing the parameterisation moves
>>>the dips around slightly. Unfortunately the PNLS step is finding a
>>>maximum at the dips rather than the mle. I have tried using starting
>>>values for the fixed parameters without change. Any ideas ?
>>
>>Ken,
>>
>>you should not use nlme for "maximising a complex function",  
>>because it's a
>>rather specialized tool for mixed-model statistical analysis. Try  
>>to use optim
>>directly, which has quite a few methods to choose from, and one of  
>>them might
>>work for your problem.
>>
>>Dieter
>>

>
>
> ______________________________________________
> R-help@stat.math.ethz.ch mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
-- 
Spencer Graves, PhD
Senior Development Engineer
PDF Solutions, Inc.
333 West San Carlos Street Suite 700
San Jose, CA 95110, USA

spencer.graves@pdf.com
www.pdf.com <http://www.pdf.com>
Tel:  408-938-4420
Fax: 408-280-7915

______________________________________________
R-help@stat.math.ethz.ch mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
Received on Tue Dec 20 03:50:54 2005

This archive was generated by hypermail 2.1.8 : Tue 20 Dec 2005 - 04:42:15 EST