[R] fitting periodic 'sine wave' model

[Søren Højsgaard]

If you make the x-values more dense, e.g. with x<-seq(0,20,0.1) then your example works. Plotting your data might give a hint to why your example fails.... Btw: It is generally not a good idea to use F for a parameter because F usually means FALSE. 
Regards
Søren

________________________________

Fra: r-help-bounces at r-project.org på vegne af Jon Loehrke
Sendt: ti 10-06-2008 16:25
Til: r-help at r-project.org
Emne: [R] fitting periodic 'sine wave' model



I have been attempting to estimate the periodic contribution of an 
effect to some data but have not been able to fit a sine wave within R.
It would be nice to start by being able to fit a sine wave with an 
amplitude and frequency.

x<-seq(0,20,by=0.5)
y<-2*sin(2*pi*.5*x) #amplitude =2, frequency=0.5

# This failed to converge
r<-nls(y ~ A*sin(2*pi*F*x), start=list(A = 1, F = 1), trace=T)


# even this gave a max iteration error
r<-nls(y ~ A*sin(2*pi*F*x), start=list(A = 1, F = .5), trace=T)

I have a feeling I am approaching this incorrectly.  Thank you all 
very much for the guidance.

Jon
R 2.7.0
mac os 10.5


Jon Loehrke
Graduate Research Assistant
Department of Fisheries Oceanography
School for Marine Science and Technology
University of Massachusetts
200 Mill Road, Suite 325
Fairhaven, MA 02719
jloehrke at umassd.edu
T 508-910-6393
F 509-910-6396

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