regression methods for circular(?) data.

On 26-Sep-05 nwew wrote:

Dear R-users,

I have the following data

x <- runif(300,min=1,max=230)

y <- x*0.005 + 0.2
y <- y+rnorm(100,mean=0,sd=0.1)
y <- y%%1 #  <------- modulo operation
plot(x,y)

and would like to recapture the slope (0.005) and intercept(0.2).
I wonder if there are any clever algorithms to do this. I was
looking at the function lm.cirucalar. Is this the method to use?
If, which of the references is best too look at?

Eryk

Hi Eryk,

If you know the modulus (in your case 1.0) and you get data that
look like the result of your "plot(x,y)", then I wouldn't mess
about.

I would simply do something like

y1<-y
ix <- ix<-(y < 0.9*(x-50)/200)
y1[ix] <- y1[ix]+1.0
lm(y1~x)

(the constants 0.9/200, -50 being chosen to give a good separation
on the graph).

On the other hand, if there are good reasons why this very simple
approach is not suitable, then if we knew what they were a more
helpful reply would be easier to formulate!

Best wishes,
Ted.


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Date: 26-Sep-05                                       Time: 15:56:48
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