Message-ID: <loom.20051218T100716-668@post.gmane.org>
Date: 2005-12-18T09:12:53Z
From: Dieter Menne
Subject: nlme problems
Ken Beath <kbeath <at> efs.mq.edu.au> 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