[R] help with nls and Hill equation

[Gabor Grothendieck]

I think its your parameterization that is problematic.

ED50^hill is tough for it to work with since both are varying.

Try reparameterizing using ED50hill = ED50^hill as a parameter
so that the parameters become Emax, ED50hill and  hill.  You
can back transform afterwards.


On 10/16/07, Lanre Okusanya <lanre.okusanya at gmail.com> wrote:
> Hello all, I am having a problem with nls. I have such data as shown below,
> foo<-
> Dose    var
> 0      0.000000
> 100  -1.318178
> 200  -1.562425
> 400  -3.579960
> 1200  -3.788662
>
> however, when I call nls as shown below,
>
> >foo.nls<-nls(var~Emax*(Dose^hill)/((EC50^hill)+(Dose^hill)),
> +                 start=list(Emax=-4,EC50=269,hill=1),trace=T,data=foo)
>
> i get the response below.
>
>      1.759088 :   -4 269   1
>    Error in numericDeriv(form[[3]], names(ind), env) :
>     Missing value or an infinity produced when evaluating the model
>
>
> if i remove the hill variable, it works. can someone help me out with
> what I am coding wrong.
>
> Thanks,
>
>
>
> Lanre
>
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