[R] problem with nls starting values

[Bert Gunter]

On Thu, Sep 27, 2012 at 12:43 PM, Benedikt Gehr
<benedikt.gehr at ieu.uzh.ch> wrote:
> now I feel very silly! I swear I was trying this for a long time and it
> didn't work. Now that I closed R and restarted it it works also on my
> machine.
>
> So is the only problem that my model is overparametrized with the data I
> have?
Probably.

> however shouldn't it be possible to fit an nls to these data?
(Obviously) no.

I suggest you do a little reading up on optimization.
Over-parameterization creates high dimensional ridges.

-- Bert



>
> thanks for the help
>
> Am 27.09.2012 21:27, schrieb Berend Hasselman:
>>
>> y_val<-115-118*exp(-0.12*(seq(1,100)+rnorm(100,0,0.8)))
>> >x_val<-seq(1:100)
>> >plot(y_val~x_val)
>>
>> > >summary(mod1<-nls(y_val~a-b*exp(-c*x_val),start=list(a=115,b=118,c=0.12)))
>> >
>
>
> --
> Benedikt Gehr
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>
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> University of Zurich
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-- 

Bert Gunter
Genentech Nonclinical Biostatistics

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