Jorge Ivan Velez wrote: > Good morning Markus, > > Perhaps ?nls might be useful in this case.
Or consult a compendium and realize that both formulas actually fit the same class of shifted sinusoidals... It holds that cos(v+phi) = cos phi cos v - sin phi sin v so you can fairly easily find A and phi from the coefficients in lm(a~cos+sin). The only reason to use nls is that it is a nonlinear transformation, so a profile-based confidence interval might be more accurate than one based on the delta method. > > HTH, > Jorge > > > On Mon, Nov 30, 2009 at 7:19 AM, Markus H�ge <> wrote: > >> Hello, >> >> the only thing I found to fit a sin/cos is s.th like lm(a~cos+sin) But >> this is not what I want. >> I have a magnitude which is sinusoidal with offset and it doesn't start >> at phi=0. >> >> The data is: >> >> angle<-c(0,10,20,30,40,50,60,70,80,90,100,110,120,130,140,150,160,170,180) >> >> Voltage<-c(-45.07, -45.24, -43.61, -40.78, -36.48, -30.92, -23.83, >> -15.95, -7.53, 1.06, 11.24,19.85, 27.00, 35.00, 42.90, 49.41, >> 54.62, 58.54, 60.90) >> >> I need an regression with Voltage=A*cos(angle+phi)+B. >> How does this work? With lm or shall I use twice Fourier? >> >> thanks >> >> Markus >> >> ______________________________________________ >> R-help@r-project.org mailing list >> https://stat.ethz.ch/mailman/listinfo/r-help >> PLEASE do read the posting guide >> http://www.R-project.org/posting-guide.html >> and provide commented, minimal, self-contained, reproducible code. >> > > [[alternative HTML version deleted]] > > > > ------------------------------------------------------------------------ > > ______________________________________________ > R-help@r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. -- O__ ---- Peter Dalgaard Øster Farimagsgade 5, Entr.B c/ /'_ --- Dept. of Biostatistics PO Box 2099, 1014 Cph. K (*) \(*) -- University of Copenhagen Denmark Ph: (+45) 35327918 ~~~~~~~~~~ - (p.dalga...@biostat.ku.dk) FAX: (+45) 35327907 ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.