From: Susan Imholt <smimholt_at_excite.com>

Date: Tue 07 Feb 2006 - 11:06:34 EST

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https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Received on Tue Feb 07 11:48:25 2006

Date: Tue 07 Feb 2006 - 11:06:34 EST

Hello,

I am trying to bootstrap a function that extracts the log-likelihood value and the nls coefficients from an nls object. I want to sample my dataset (pdd) with replacement and for each sampled dataset, I want to run nls and output the nls coefficients and the log-likelihood value.

Code:

x<-c(1,2,3,4,5,6,7,8,9,10)

y<-c(10,11,12,15,19,23,26,28,28,30)

pdd<-data.frame(x,y)

i<-sample(10, replace=TRUE)

pdd.lik.coef<-function(data,i){

d<-data[i,] pdd.nls<-nls(d$y~(a*(d$x)^2)/(b+(d$x)^2), data=pdd, start = list(a = 30, b = 36), trace=FALSE) pdd.logLik<-logLik(pdd.nls) coeff <- coef(pdd.nls) lik.coef <- c(pdd.logLik, coeff)

}

pdd.boot<-boot(data=pdd, statistic=pdd.lik.coef, R=1000) pdd.boot$t

My problem lies in the pdd.lik.coef function. It seems that nls recognizes all letters in the formula d$y~(a*(d$x)^2)/(b+(d$x)^2) as parameters, so "d$y" and "d$x" in the formula aren't being recognized properly to be sampled, rather the "d" is interpreted as a parameter. When I try to bootstrap this function, I get an error message: "Error in eval(expr, envir, enclos) : object "d" not found" (because I didn't specify an estimate for d as a parameter, since I didn't intend for it to be a parameter).

Any suggestions?

Thanks,

Susie Imholt

Master's Candidate

Huxley College of the Environment

Western Washington University

Bellingham, WA USA

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https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Received on Tue Feb 07 11:48:25 2006

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