[R] weights in nls

[ben@zoo.ufl.edu]

  Thanks for your help.

  Ben Bolker


On 26 Sep 2000, Douglas Bates wrote:

> Douglas Bates <bates at cs.wisc.edu> writes:
> 
> > In the meantime, you can use the approach that John Chambers and I
> > describe in chapter 10 of "Statistical Models in S" (a.k.a. the white
> > book) and write the model as a one sided formula giving the weighted
> > residual.
> 
> I should have checked before I wrote that.  A one-sided formula
> doesn't work.  You must use a vector of zeroes of the appropriate
> length on the left hand side.
> 
> > library(nls)
> > data(Puromycin)
> > nls(rate ~ Vm * conc/(K + conc), data = Puromycin, weights = 1/conc, 
> +    subset = state == "treated", start = c(Vm = 200, K = 0.05))
> Nonlinear regression model
>   model:  rate ~ Vm * conc/(K + conc) 
>    data:  Puromycin 
>           Vm            K 
> 212.68357970   0.06412103 
>  residual sum-of-squares:  1195.449 
> > nls(rep(0, length(conc)) ~ (rate - Vm * conc/(K + conc))* sqrt(conc), 
> +   data = Puromycin, subset = state == "treated", start = c(Vm = 200, K = 0.05))
> Nonlinear regression model
>   model:  rep(0, length(conc)) ~ (rate - Vm * conc/(K + conc)) * sqrt(conc) 
>    data:  Puromycin 
>           Vm            K 
> 218.15162032   0.07471006 
>  residual sum-of-squares:  137.4447 
> 
> 

-- 
318 Carr Hall                                bolker at zoo.ufl.edu
Zoology Department, University of Florida    http://www.zoo.ufl.edu/bolker
Box 118525                                   (ph)  352-392-5697
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