From: Rick DeShon <deshon_at_msu.edu>

Date: Tue, 06 May 2008 16:50:11 -0400

R-help_at_r-project.org mailing list

https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code. Received on Tue 06 May 2008 - 20:53:22 GMT

Date: Tue, 06 May 2008 16:50:11 -0400

I've run into a problem with the plinear algorithm in nls that is confusing me.

0 1132.0 1 630.5 2 1371.5 3 704.0 4 488.5 5 575.5 6 613.0 7 824.5 8 509.0 9 791.0 10 492.5 11 515.5 12 467.0 13 556.5 14 456.0

Now fit a power function to this data using nls with the plinear algorithm

*>fit.pw <-nls(RT ~ cbind(1,trl, trl^p), start = c(p = -.2), algorithm =
*

"plinear", data=df.one)

Yields the following error message....

"Error in numericDeriv(form[[3]], names(ind), env) :

Missing value or an infinity produced when evaluating the model"

Now, recode trial from 1-15 and run the same model.

*>fit.pw <-nls(RT ~ cbind(1,trl, trl^p), start = c(p = -.2), algorithm =
*

"plinear", data=df.one)

Seems to work fine now...

Nonlinear regression model

model: RT ~ cbind(1, trl, trl^p)

data: df.one

p .lin1 .lin.trl .lin3 -0.2845 200.3230 -8.9467 904.7582 residual sum-of-squares: 555915

Number of iterations to convergence: 11

Any idea why having a zero for the first value of X causes this problem?

Thanks in advance,

Rick DeShon

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