Hi Bill, I've just spent a few months trying to fit a model to a dataset, and it's not easy. However, in my case, what appears to be recalcitrance on R's part actually turns out to be well-founded warnings that the structure of the model and the data are not permitting a clean, unambiguous fit.
I warmly recommend the Bates and Watts book on non-linear regression analysis, and also Venables and Ripley MASS, with especial reference to the online complements. My strategy to learn more about my problem was: increase "tol" and decrease minFactor until I get a fit, and then examine the intrinsic and parameter curvatures using the rms.curv() function in the MASS package. It showed quite clearly that there was a real problem with the parameterization of the model. Of course, using that particular fit was out of the question. I recommend against trying another tool: instead, learn more about this one and why it's behaving in that way. Good luck. Andrew On Thursday 01 April 2004 07:37, Bill Shipley wrote: > Hello. I am trying to fit a non-rectangular hyperbola function to data > of photosynthetic rate vs. light intensity. There are 4 parameters that > have to be estimated. I find the nls function very difficult to use > because it often fails to converge and then gives out cryptic error > messages. I have tried playing with the control parameters but this > does not always help. > > Is there another non-linear regression function in R that I might try > (other than regression smoothers, which won�t give the parameter > estimates of the specified function)? > > > > Bill Shipley > > Subject Matter Editor, Ecology > > North American Editor, Annals of Botany > > D�partement de biologie, Universit� de Sherbrooke, > > Sherbrooke (Qu�bec) J1K 2R1 CANADA > > [EMAIL PROTECTED] > > <http://callisto.si.usherb.ca:8080/bshipley/> > http://callisto.si.usherb.ca:8080/bshipley/ > > > > > [[alternative HTML version deleted]] > > ______________________________________________ > [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 -- Andrew Robinson Ph: 208 885 7115 Department of Forest Resources Fa: 208 885 6226 University of Idaho E : [EMAIL PROTECTED] PO Box 441133 W : http://www.uidaho.edu/~andrewr Moscow ID 83843 Or: http://www.biometrics.uidaho.edu No statement above necessarily represents my employer's opinion. ______________________________________________ [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
