# [R] weights in nls

ben@zoo.ufl.edu ben at zoo.ufl.edu
Tue Sep 26 19:21:15 CEST 2000

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
>
>

--
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Zoology Department, University of Florida    http://www.zoo.ufl.edu/bolker
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