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
