[R] nls vs nlme: parameter constraints

Manuel Morales Manuel.A.Morales at williams.edu
Mon Jun 22 23:50:08 CEST 2009


Hello list,

I'm trying to fit a model like beta[trt]/(1+alpha*x) where the data
include some grouping factor. The problem is that the estimate for alpha
is undefined for some of the treatments - any value greater than 20 is
equally good and a step function would suffice. Ignoring the grouping
structure, I can fit this using nls with the port algorithm by
restricting the upper value of alpha to 20. Is there a way to do
something similar in nlme?

Thanks!

Manuel

-- 
http://mutualism.williams.edu




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