cstrato <[EMAIL PROTECTED]> writes: > 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?
The expression only depends on a/b so you cannot estimate both. Besides, you need to check up on operator precedence and associativity: What you wrote is equivalent to a*sin(x)*x/b. -- O__ ---- Peter Dalgaard Blegdamsvej 3 c/ /'_ --- Dept. of Biostatistics 2200 Cph. N (*) \(*) -- University of Copenhagen Denmark Ph: (+45) 35327918 ~~~~~~~~~~ - ([EMAIL PROTECTED]) FAX: (+45) 35327907 ______________________________________________ [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