[R] non-linear model parameterization

Gabor Grothendieck ggrothendieck at gmail.com
Mon Oct 1 04:08:25 CEST 2007

The model is not identifiable since if (a, b, g) is a solution then
so is every multiple of it.

On 9/30/07, Irene Mantzouni <ima at difres.dk> wrote:
> Dear all,
> I would like to fit a non-linear model of the form:
> y=g*x/(a+b*x)
> with nls().
> However this model is somehow overparameterized and I get the error message about
> singular gradient matrix at initial parameter estimates.
> What I am interested in is to make inference about parameters b and g, so this has to be taken into account in the model formulation.
> What options do I have?
> Also, how is it possible to fit a partially linear model?
> Thank you!!
> Irene Mantzouni
> ----------------
> PhD student
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