From: Peter Dalgaard <p.dalgaard_at_biostat.ku.dk>

Date: Thu 01 Jul 2004 - 00:04:00 EST

Date: Thu 01 Jul 2004 - 00:04:00 EST

Douglas Bates <bates@stat.wisc.edu> writes:

*> Often when nls doesn't converge there is a good reason for it.
**>
**> I'm on a very slow internet connection these days and will not be able
**> to look at the data myself but I ask you to bear in mind that, when
*

> dealing with nonlinear models, there are model/data set combinations

> for which there are no parameter estimates.

In this particular case, the model describes a curve consisting of two line segments that meet at the point (b,d)

> > : nls(y~d+(x-b)*c1*(x-b<0)+(x-b)*c2*(x-b>=0), data=df2,

Now if b is between the two smallest x, you can diddle b, c1, and d in such a way that the value at x1 is constant. I.e. the model becomes unidentifiable. Putting trace=T suggests that this is what happens in this example.

-- O__ ---- Peter Dalgaard Blegdamsvej 3 c/ /'_ --- Dept. of Biostatistics 2200 Cph. N (*) \(*) -- University of Copenhagen Denmark Ph: (+45) 35327918 ~~~~~~~~~~ - (p.dalgaard@biostat.ku.dk) FAX: (+45) 35327907 ______________________________________________ R-help@stat.math.ethz.ch mailing list https://www.stat.math.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.htmlReceived on Thu Jul 01 00:08:22 2004

*
This archive was generated by hypermail 2.1.8
: Fri 18 Mar 2005 - 04:45:31 EST
*