On Dec 20, 2010, at 3:01 PM, Paolo Rossi wrote:
Hi everyone,
I am trying to fit a sine function on one year of wind data. I have
two
questions below.
Looking around on the net I managed to get the following:
Sine Equation: y = a + b * sin( c + d*x )
b is the amplitude, c is the phase shift, d is something deal with
periodicty of data*.*
This can be linearised by sin( c+dx ) = cos(c) * sin(dx) + sin(c) *
cos(dx).
If one calls dx = x1
y = a + b * sin( c + d*x )
y = a + b * [cos(c) * sin(x1) + sin(c) * cos(x1)]
y = a + b * cos(c) * sin(x1) + b * sin(c) * cos(x1)
y = a + b1 * sin(x1) + b2 * cos(x1)
where b1 = b * cos(c) and b2 = b * sin(c)
This works fine for me as I am not interested in the value for b and
c. By
trial and error I also detemined that the sensibel value for d is
1/58. I
have 366 days of data and want to fit a single sine onto it.
*First question*: 1/ 58 = (2 pi) / 366. I guess 366 is the period of
my
data, I have 366 days. so *d = (2 pi) / Period*. Is this correct.
*Second question*: I reckon that all of this looks very DIY. Is
there a
better way to do this in R? Maybe through a package I dont know?
The package "circular" might be a candidate.
Thanks in advance
Paolo
David Winsemius, MD
West Hartford, CT
______________________________________________
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.
