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Overview of AFOF

Afof is an approximate group finder, which uses the friends-of-friends method to find groups. A particle belongs to a friends-of-friends group if it is within some linking length tau of some other particle in the group. The algorithm is approximate. It takes an additional parameter epsilon which indicates how much error can be tolerated. The error will take the form of over-linking. All lengths at most tau will be linked and all lengths greater than (1 + epsilon)tau will not be linked. Lengths between tau and (1 + epsilon)tau may or may not be linked. More information on the algorithm used in afof can be found here. After all such groups are found, those with less than a specified minimum number of group members are rejected. The program takes input files in the tipsy binary format and produces a single ASCII output file called afof.grp. This output file is in the tipsy array format and contains the group number to which each particle belongs. A group number of zero means that the particle does not belong to a group. The afof.grp file can be read in by tipsy and used to color each particle by group number. This provides an effective way to visualize the groups that are found by afof. Simulations with periodic boundary conditions can also be handled by afof by specifying the period in each dimension on the command line (see MAN page below).

To obtain afof, get the tar file from our Anonymous ftp-site at The relevant tar file is /pub/hpcc/afof.0.9.tar.Z.

To build afof,

zcat afof.0.9.tar.Z | tar xfv -


This should build afof on most systems.

See MAN page for help on using afof.

For more information on afof please send mail to

N-Body Shop
University of Washington
Box 351580
Seattle, WA  98195-1580
(206) 543-2888 voice, (206) 685-0403 FAX
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