Sorry, I forgot to mention that you have also indicated that I have only one parameter. Fitting using lm gives: c=1.023 w/o and c=1.146 with outliers.
Maybe sin(x)/x was a bad example, how about trying to fit a polynomial of degree n?
Best regards Christian
Ravi Varadhan wrote:
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 _._._._._._._._._._._._._._._._
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