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
jlabo...@huskers.unl.edu
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