[R] Singular Gradient

[Douglas Bates]

On 2/7/07, This Wiederkehr <this.wiederkehr at gmail.com> wrote:
> I tried to fit data with the following function:
>
> fit<-nls(y~ Is*(1-exp(-l*x))+Iph,start=list(Is=-2e-5,l=2.3,Iph=-0.3
> ),control=list(maxiter=500,minFactor=1/10000,tol=10e-05),trace=TRUE)
> But I get only a singular Gradient warning...

Did you get any trace output at all?  It is not clear if you got the
singular gradient warning before the first iteration completed, which
means there is a problem at the starting estimates, or after a few
iterations.  Without the data it is difficult to decide.

> the data can by found attached(there are two sampels of data col 1/2 and
> 3/4).

Thanks for offering to include the data.  My copy of your message did
not have the data enclosed.  Did you perhaps forget to attach the
file?

 > I tried to fix it by chanching the start parameters but that didn't solve
> the problem.

> Would it be a possibiliti to use the selfstart Model? How?

Yes.  Try SSasymp.  I believe that model is equivalent to your model
but in a different parameterization.


> Thanks for any answers
>
> This
>
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