[R] Robust nonlinear regression - sin(x)/x?

[Ravi Varadhan]

A small correction to my previous email:
You actually specify the following call to lm:

y <- sin(x)/x
lm(z ~ y - 1)

to make sure that the intercept is not estimated.

Ravi.

----- Original Message -----
From: Ravi Varadhan <rvaradha at jhsph.edu>
Date: Monday, February 2, 2004 2:46 pm
Subject: Re: [R] Robust nonlinear regression - sin(x)/x?

> You reall have only one parameter in your model, c = a/b. You 
> can't 
> identify both a and b from your model, therefore, you should fit 
> the 
> linear model:  lm(z ~ c* sin(x)/x)
> 
> Ravi.
> 
> ----- Original Message -----
> From: cstrato <cstrato at aon.at>
> Date: Monday, February 2, 2004 2:28 pm
> Subject: [R] Robust nonlinear regression - sin(x)/x?
> 
> > Dear all
> > 
> > Since I did not receive any answer to my general question (?),
> > let me ask a concrete question:
> > 
> > How can I fit the simple function y = a*sin(x)/b*x?
> > 
> > This is the code that I tried, but nls gives an error:
> > 
> > x <- seq(1,10,0.1)
> > y <- sin(x)/x
> > plot(x,y)
> > z <- jitter(y,amount=0.1)
> > plot(x,z)
> > df <- as.data.frame(cbind(x,z))
> > nf <- nls(z ~ a*sin(x)/b*x, data=df,
> >           start=list(a=0.8,b=0.9), trace = TRUE)
> > 
> > I have followed the Puromycin sample which works fine:
> > Pur.wt <- nls(rate ~ (Vm * conc)/(K + conc), data = Treated,
> >               start = list(Vm = 200, K = 0.1), trace = TRUE)
> > 
> > Do I make some mistake or is it not possible to fit sin(x)/x?
> > 
> > Thank you in advance
> > Best regards
> > Christian
> > _._._._._._._._._._._._._._._._
> > C.h.i.s.t.i.a.n S.t.r.a.t.o.w.a
> > V.i.e.n.n.a       A.u.s.t.r.i.a
> > _._._._._._._._._._._._._._._._
> > 
> > 
> > cstrato wrote:
> > > Dear R experts
> > > 
> > > This is a general question:
> > > Does R have functions for nonlinear robust regression,
> > > analogous to e.g. LTS?
> > > 
> > > Searching google I have found
> > > 1, an abstract to generalize LTS for nonlinear regression
> > > models, see: http://smealsearch.psu.edu/1509.html
> > > 2, an AD-model builder, see: http://otter-
> rsch.com/admodel/cc1.html> > but no mention of R/S
> > > 
> > > Thank you in advance
> > > Best regards
> > > Christian
> > > _._._._._._._._._._._._._._._._
> > > C.h.i.s.t.i.a.n S.t.r.a.t.o.w.a
> > > V.i.e.n.n.a       A.u.s.t.r.i.a
> > > _._._._._._._._._._._._._._._._
> > > 
> > > ______________________________________________
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> > > PLEASE do read the posting guide! 
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> > > 
> > >
> > 
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