With that simplification, the equation is linear.
However, I see another problem: If x is 0, sin(x)/x is "NaN". For a situation like this, I typically write a function to first compute "sin(x)/x", then test for x being 0 or very small, and replace the value in such cases with a more accurate Taylor series or asymptotic expansion.
hope this helps. spencer graves
cstrato wrote:
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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