I wanted to use the nls() module to solve a Problem from Sen & Srivastava 
(1990, p.209). Here is the (basic) code used to perform the estimation:

library(SenSrivastava)
library(nls)
data(E9.8)

# Use Linear Least Square for estimating start values
lm.obj <- lm(R.1 ~ I.1 + S.1, data = E9.8)

nls1.obj <- nls(R.1 ~ b.0 + b.1*(I.1^a.1-1)/a.1 + b.2*(S.1^a.2-1)/a.2,
                         data = E9.8,
                         start = list(b.0 = coef(lm.obj)[1], b.1 = 
coef(lm.obj)[2], b.2 = coef(lm.obj)[3],                       a.1 = 1, a.2 = 1)
                    )

unfortunately, I receive the following message from nls(): "Error in 
object[[i]] : object is not subsettable"

Why do I get this message, what does it mean, and how can I avoid it ?
Note 1: Enclosing expressions by using the function I() does not help either.
Note 2: To avoid confusion I have changed the names I, R, S to I.1, R.1, S.1.

Sincerely,
Siegfried Macho




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Dr. Siegfried Macho
Department of Psychology
University of Fribourg
Rue de Faucigny 2
CH-1700 Fribourg

Tel.: +41-26-3007635
Fax.: +41-26-3009712
http://www.unifr.ch/psycho/general/macho.htm
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