[Rd] extracting and manipulating components from nlme and gnls objects

Nicholas Lewin-Koh nikko at hailmail.net
Tue Jul 19 19:32:40 CEST 2005

Yes, I looked more carefully at the code and realized the parameters
have to be named
and then the gradient is returned so that
SSlogis(3.4,4,5,6) does not return the gradient as an attribute but


However what I am finding more vexing is if I fit a model, say

fit<-gnls(resp~SSlogis(covar,Asym,xmid,scal), data=foo,

and I want to evaluate the arbitrary variance function at a new x, x0
then how do i get the variance function from the fit object and evaluate
at f(x0,..)?

So far I can predict at x0 using predict(fit, newdata=list(covar=x0)) to
get the fitted value
but how to I plug that in to the varStruct stored in fit$modelStruct?

On Tue, 19 Jul 2005 11:48:18 -0500, "Douglas Bates" <dmbates at gmail.com>
> On 7/19/05, Nicholas Lewin-Koh <nikko at hailmail.net> wrote:
> > Hello,
> > I am writing a set of functions to do prediction and calibration
> > intervals
> > for at least the subset of selfstarting models if not some more general
> > ones.
> > 
> > I need to be able to extract the varFunction from a fit object
> > and evaluate it at a predicted point. Are there any examples around?
> > 
> > Also in a self start model, say SSlogis, how would I get the gradient
> > at a point?
> I think that the output of 
> example(SSlogis)
> should answer that question for you.

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