Thank you all very much for your help. Unfortunately I do not have the data to test out the ideas suggested but I was able to find a good approximation using another software package. I will try to get the data for this problem so I can find out how to do it in R as I am very much interested in the process.
@Dennis : Indeed, its the c that causes the problem. Without the c, solving this would be a very easy thing. On Mon, Sep 13, 2010 at 12:01 PM, Greg Snow <[email protected]> wrote: > Without the square term you can just use the rule for addition in sines: > > sin(a+b) = sin(a)cos(b) + cos(a)sin(b) > > So a regression of y= a + b* sin(2*pi/360*x + c) can be fit as: > > lm( y~ sin( 2*pi/360*x) + cos( 2*pi/360/x ) ) > > If you need the actual values of b and c then you will need to do a little > algebra. > > The same idea may be sufficient for your formula (or at least a close > approximation), or you could switch to nonlinear fits using the nls function > and fit your formula directly. > > -- > Gregory (Greg) L. Snow Ph.D. > Statistical Data Center > Intermountain Healthcare > [email protected] > 801.408.8111 > > > > -----Original Message----- > > From: [email protected] [mailto:r-help-boun...@r- > > project.org] On Behalf Of Aaditya Nanduri > > Sent: Sunday, September 12, 2010 8:23 PM > > To: [email protected] > > Subject: [R] How to do a trig regression > > > > Hello All, > > > > I cant seem to do a trig regression in R. > > > > The equation is as follows : y = a+b*(sin((2*pi*x/360) - c))^2 > > > > a, b, c are coefs that I want. > > y, x are input vectors. > > > > The equation I put into R: lm(y ~ sin(2*pi*x/360)^2) > > This equation is missing the c and I dont get the right answer. > > > > Also, I dont know how to plot the lm over the x values instead of the > > indices. > > > > Any help is sincerely appreciated. > > Thank you all very much. > > > > -- > > Aaditya Nanduri > > [email protected] > > > > [[alternative HTML version deleted]] > > > > ______________________________________________ > > [email protected] 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. > -- Aaditya Nanduri [email protected] [[alternative HTML version deleted]] ______________________________________________ [email protected] 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.
