Nonlinear weighted least squares estimation

Hi Robert

	You can try gnls() in the nlme package or if that is not suitable, try to
follow the example in the nls() help page for weighted regression that has
an example of weighted regression from MASS.

from the nls help page:


     ## weighted nonlinear regression
     Treated <- Puromycin[Puromycin$state == "treated", ]
     weighted.MM <- function(resp, conc, Vm, K)
     {
         ## Purpose: exactly as white book p.451 -- RHS for nls()
         ##  Weighted version of Michaelis-Menten model
         ## ------------------------------------------------------------
         ## Arguments: 'y', 'x' and the two parameters (see book)
         ## ------------------------------------------------------------
         ## Author: Martin Maechler, Date: 23 Mar 2001, 18:48

         pred <- (Vm * conc)/(K + conc)
         (resp - pred) / sqrt(pred)
     }

     Pur.wt <- nls( ~ weighted.MM(rate, conc, Vm, K), data = Treated,
                   start = list(Vm = 200, K = 0.1),
                   trace = TRUE)


regards,

Jesus

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Jes??s Mar??a Fr??as Celayeta
School of Food Sci. and Env. Health.
Faculty of Tourism and Food
Dublin Institute of Technology
Cathal Brugha St., Dublin 1. Ireland
t +353 1 4024459 f +353 1 4024495
w www.dit.ie/DIT/tourismfood/science/staff/frias.html
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Nonlinear weighted least squares estimation

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