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Overview of FOF

Fof is a simple 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 of any other particle in the group. 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 fof.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 fof.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 fof. Simulations with periodic boundary conditions can also be handled by fof by specifying the period in each dimension on the command line (see MAN page below). For a more sophisticated group finding code, see the denmax program.

Release 1.1 new features

Improvement in tree building part of the code. This new version produces better balanced trees and is more robust (a few rare cases caused problems).

To obtain fof, get the tar file from our Anonymous ftp-site at The relevant tar file is /pub/hpcc/fof-1.1.tar.Z.

To build fof,

zcat fof-1.1.tar.Z | tar xfv -


This should build fof on most systems.

See MAN page for help on using fof.

Support for this software is now being hosted on SourceForge. For problems, questions and comments concerning this software, please go to the SourceForge Astrophysical N-body Tools site.

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