Re: [R] newbie nls question

From: Michael Manning <michael.manning_at_niwa.co.nz>
Date: Wed, 11 Jun 2008 11:08:21 +1200

Hi

On 11/06/2008 at 10:56 a.m., "Ranney, Steven" <steven.ranney_at_montana.edu> wrote:
> I'm tyring to fit a relatively simple nls model to some data, but keep coming
> up against the same error (code follows):
>
> Oto=nls(Otolith ~ Linf*(1-exp(-k(AGE-to))),
> data = ages,
> start = list(Linf=1000, k=0.1, to=0.1),
> trace = TRUE)
>
> The error message I keep getting is "Error in eval(expr, envir, enclos) :
> could not find function "k"". I've used this line of code for other nls
> models (with different data, parameter estimates, etc.), but have never
> gotten this error. The data is
>
> AGE,Otolith,Scale
> 1,207.1052632,207.1052632
> 2,329.962963,332.7586207
> 3,401.9473684,406
> 4,422,413.1111111
> 5,452.6785714,458.34375
> 6,510.75,533
> 7,477,674
> 8,643,704
> 9,,615
> 10,695.5,
> 12,615,
>
> Are the missing values (e.g., no value for Otolith, AGE 9) having an effect?
> I am using Tinn-R as an editor
>
> I'm new to R, trying to get away from Rcmdr (though it has been helpful),
> and still trying to learn the language with the aid of several books on the
> R. A search of the R Archive did not prove fruitful.
>
> Thanks in advance,
>
> SR
>
> Steven H. Ranney

You've made a typo.

Check out the formula you passed to nls -- you forget to include a "*" after k.

What I think you want is something like

Oto <- nls(Otolith ~ Linf * (1 - exp(-k * (AGE - t0) ) ), ...)

Cheers,

Michael



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Received on Tue 10 Jun 2008 - 23:42:47 GMT

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