(no subject)

Please read the posting guide and use a sensible subject line, tell us 
about the R version you are using, and add a *reproducible* example.

We get:

Error in nls(npe ~ SSgompertz(npo, Asym, b2, b3), data = f, control = 
nls.control(maxiter = 500)) :
   object 'f' not found

Best,
Uwe Ligges

Hi,

I am using the nls function and it stops because the number of iterations
exceeded 50, but i used the nls.control argument to allow for 500
iterations. Do you have any idea why it's not working?

fm1 <- nls(npe ~ SSgompertz(npo, Asym, b2, b3),
data=f,control=nls.control(maxiter=500))

Error in nls(y ~ exp(-b2 * b3^x), data = xy, algorithm = "plinear", start =
c(b2 = pars[["b1"]],  :
   number of iterations exceeded maximum of 50

Thanks for your help,
Cheers,
Karine.

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I am using the nls function and it stops because the number of iterations
exceeded 50, but i used the nls.control argument to allow for 500
iterations. Do you have any idea why it's not working?

Not entirely. But I do see in the code for SSgompertz that SSgompertz calls nls _without_ specifying maxiter. So I suspect the error may be coming from the selfstart step which is ignoring your control argument.

You could check that by adding trace=TRUE to the nls call; I suspect you may see no iterations at all if the self-start fails before nls itself gets going. 

If that's so, the easiest way I can see round that (barring alrternative packages I've not heard of) is to copy the SSgompertz code to a text file (say 'SSgompertz' at the command line without () to see the code), create your own SSgompertz function from it, add a big maxiter in its internal call and use your version.

Failing that, use good starting parameters (usually I fool around with plots until something looks close enough to at least start) for a roll-your-own gompertz model.

S Ellison

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