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 <Greg.Snow@imail.org> 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
> greg.snow@imail.org
> 801.408.8111
>
>
> > -----Original Message-----
> > From: r-help-bounces@r-project.org [mailto:r-help-bounces@r-
> > project.org] On Behalf Of Aaditya Nanduri
> > Sent: Sunday, September 12, 2010 8:23 PM
> > To: r-help@r-project.org
> > 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
> > aaditya.nanduri@gmail.com
> >
> >       [[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.
>



-- 
Aaditya Nanduri
aaditya.nanduri@gmail.com

	[[alternative HTML version deleted]]

