Douglas Bates <[EMAIL PROTECTED]> 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 ~~~~~~~~~~ - ([EMAIL PROTECTED]) FAX: (+45) 35327907 ______________________________________________ [EMAIL PROTECTED] 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.html
