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[S] Question on weighted non linear regression

To: "s-news-digest@wubios.wustl.edu" <s-news-digest@wubios.wustl.edu>
Subject: [S] Question on weighted non linear regression
From: Abd Rahman Kassim <rahmank@frim.gov.my>
Date: Mon, 28 Feb 2000 04:36:13 +0800
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Dear S-Plus Users,

I am analysing data using nls regression at different weight. I've tested 
the two similar forms of nls function:  

a) nls.fm0 <- nls( (~sqrt(bat^0)*(bag -(b0* bat^b2 * exp(b1 * bat + b3 * 
idp1 + b4 *
                idp2+ b5 * idp3 + b6 * idp4 + b7 * idp5)))), start = nls.st, 
trace = T)

b) nls.fm0 <- nls( ((bag ~(b0* bat^b2 * exp(b1 * bat + b3 * idp1 + b4 *
                idp2+ b5 * idp3 + b6 * idp4 + b7 * idp5)))), start = nls.st, 
trace = T)

but I get different  results for the root mean square error (rmse). Is the 
function wrongly written? What would be the correct code ? I would like to 
test for weight equal bat^1, bat^2, bat^3 before deciding the final model.

Any comment is appreciated.

Abd Rahman Kassim
(Senior Research Officer)
Hill Forest Silviculture
Forest Research Institute Malaysia (FRIM)
Kepong 52109
Kuala Lumpur

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