[R] nlme problems

Ken Beath kbeath at efs.mq.edu.au
Sat Dec 17 22:54:58 CET 2005

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 ?


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