Particle tracking using IDL -- John C. Crocker and
Eric R. Weeks
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IDL routines to calculate the pair correlation function g(r)
Slight revision July 22, 2005 -- fixed a bug when rmax is an
integer rather than a float
Slight revision June 14, 2005 -- fixed a bug in the plotting,
which did not affect the output data, fortunately!
IDL> gr = ericgr2d(data)
The default is to assume the data is in the form (x,y, --- ,t)
where the first two columns are positions, the next few columns
are arbitrary (and could be missing), and the last column is a
timestamp. If you have tracked data:
IDL> gr = ericgr2d(data,/track)
There are other options as well. The default is to calculate
g(r) for 0 < r < 10, with a spacing of every 0.01. (See here for brief explanation.) To
override this, you can use the following keywords:
IDL> gr = ericgr2d(data,rmin=1.0,rmax=100.0,deltar=0.1)
It's used exactly the same as the 2D program. The coding
is quite different, though, for boring
technical reasons, thus you have to use a different program.
One warning that's only for ericgr3d: again due to boring
technical reasons, you shouldn't set rmax to be
more than half of the spatial extent of your data in X
and Y. ericgr2d doesn't have this problem.
This program plots an update of g(r) at each step, which
you can prevent with the /noplot keyword.
- What is the pair correlation function?
- How to calculate g(r)
- IDL routines to calculate g(r)
(you are here)
- Extra g(r) routines -- unsupported
- This page was written by