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 <[EMAIL PROTECTED]> 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 <[EMAIL PROTECTED]> > 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 > > > _._._._._._._._._._._._._._._._ > > > > > > ______________________________________________ > > > [EMAIL PROTECTED] mailing list > > > https://www.stat.math.ethz.ch/mailman/listinfo/r-help > > > PLEASE do read the posting guide! > > > http://www.R-project.org/posting-guide.html > > > > > > > > > > ______________________________________________ > > [EMAIL PROTECTED] mailing list > > https://www.stat.math.ethz.ch/mailman/listinfo/r-help > > PLEASE do read the posting guide! http://www.R- > project.org/posting- > > guide.html > > ______________________________________________ > [EMAIL PROTECTED] mailing list > https://www.stat.math.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide! http://www.R-project.org/posting- > guide.html ______________________________________________ [EMAIL PROTECTED] mailing list https://www.stat.math.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
