jlaborde at huskers.unl.edu
2014-May-20 10:41 UTC
[R] Fitting multiple nonlinear regression lines with nlrob()
Greetings R community, I would like to regress a nonlinear trend onto several subsets of data (representing different treatments) within a dataset. In my case, I would like to fit a nonlinear trend to several different "Tillage" treatments. model.global = nlrob(FinalBiomass ~ Wm[Tillage]*(1-exp((DVS/a[Tillage])^b[Tillage])), data=DATA, start = list(Wm=c(350,350,350), a=c(1.4,1.4,1.4),b=c(2.3,2.3,2.3) ), trace=TRUE)? I can do this no problem with nls(), however, when I try to do this with nlrob() I get the error message: Error in nls(formula, data = data, start = start, algorithm = algorithm, : parameters without starting value in 'data': Wm, a, b ?However, I thought I had defined the starting values for my parameters in my code (I have 3 "Tillage" treatments I am trying to fit). I do get an output, but it is identical to the output I get when I run nls(). Is nlrob capable of performing this analysis?? Any thoughts would be appreciated. Best, John John Laborde Graduate Research Assistant University of Nebraska-Lincoln Department of Agronomy & Horticulture jlaborde@huskers.unl.edu [[alternative HTML version deleted]]