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
--------------------------------------------------------------
Jesús María Frías 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
--------------------------------------------------------------
> -----Original Message-----
> From: [EMAIL PROTECTED]
> [mailto:[EMAIL PROTECTED] Behalf Of Robert Brown FM
> CEFAS
> Sent: 08 November 2004 15:03
> To: [EMAIL PROTECTED]
> Subject: [R] Nonlinear weighted least squares estimation
>
>
> Hi there,
>
> I'm trying to fit a growth curve to some data and need to use a
> weighted least squares estimator to account for
> heteroscedasticity in the data. A weights argument is available
> in nls that would appear to be appropriate for this purpose, but
> it is listed as 'not yet implemented'. Is there another package
> which could implement this procedure?
>
> Regards,
>
> Robert Brown
>
> ______________________________________________
> [EMAIL PROTECTED] mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide!
> http://www.R-project.org/posting-guide.html
>
> --
> This message has been scanned for content and
> viruses by the DIT Information Services MailScanner
> Service, and is believed to be clean.
> http://www.dit.ie
>
--
This message has been scanned for content and
viruses by the DIT Information Services MailScanner
Service, and is believed to be clean.
http://www.dit.ie
______________________________________________
[EMAIL PROTECTED] mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
