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help for circcentre
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Centring circular data

        circcentre varname [if exp] [in range] , generate(newvar)
                 [centre(centre) sine ]


Description

    circcentre takes varname, a circular variable between 0 and 360 degrees,
    and produces a new variable newvar centring varname on the direction(s)
    given by centre(). If centre() is not specified, circcentre looks for a
    vector mean left behind by circsummarize as r(vecmean).  newvar varies
    from -180 degrees to 180 degrees, with centre at 0 degrees.


Options

    generate() specifies the name of the new variable and is not optional.

    centre() specifies the direction(s) which correspond to the centre(s) of
        newvar. Possibilities are various constants or the name of a variable
        containing one or more directions.

    sine specifies that the new variable be expressed on a sine scale,
        precisely as sine of (varname - centre) / 2. This transformation
        pulls in the tails and pushes out the middle of the distribution. For
        examples of this transformation, see Fisher (1993).


Examples

    . circsummarize wallasp
    . circcentre wallasp, gen(wallasp2)
    . circcentre wallasp, gen(wallasp3) centre(45)

    . circcentre orient, gen(relflow) centre(iceflow)


Author

    Nicholas J. Cox, University of Durham, U.K.
    n.j.cox@durham.ac.uk


References

    Fisher, N.I. 1993. Statistical analysis of circular data.  Cambridge:
        Cambridge University Press.


Also see

    On-line:  help for circdiff, circsummarize