The GREAL software builds a tree from a collection of sets.  The input is a Boolean nxm matrix H,
with H[i][j] = 1 iff set i contains element j. The output is a tree with edges labeled 0,…m-1 such 
that every set (a row of H) indicates the labels in some path in the tree.

Input:
H is given in a file named by default “hypergraph.txt”. 
Every line in the file is a row of H, containing m 0s and 1s separated by spaces or tabs. 
The input file must reside in the same folder from which you run GREAL. To change the name of 
the input file use the ‘-i’ option in the command line (see below). 

Output:
GREAL outputs several files, most of which are for internal use. The names of the files that 
concern the user are preceded by “RESULT_”.
RESULT_realization.txt: 
This file contains the resulting tree, as an edge key followed by an adjacency matrix of the 
tree. The key is needed in case multiple columns in H match the same edge in the tree. 
Every line in the key has the format “x = x, y, z, w,….”. 
The adjacency matrix A has both columns and rows of indexed by the vertices of the tree. A[i][j] 
is -1 if vertices i and j are not connected by an edge. A[i][j] is a non-negative integer k if 
vertices i and j are connected by an edge with key k. If the key for edge x was “x = x, y, z”, 
then there are i, j such that A[i][j] = x and the actual labels of the edge between i and j are 
x, y and z. 
If there is no realization for the hypergraph, this file will contain only the line 
“NO REALIZATION”.
RESULT_neato_format.txt: 
This file contains the resulting tree in the input format of the neato software (see below).
The output files will be saved to the folder from which you run GREAL. To change the default 
name of the output files use the ‘-o’ and ‘-no’ options in the command line respectively (see 
below). 

Parameters:
GREAL takes three optional parameters:
‘-i file-name’ :  Input file (default: ‘hypergraph.txt’)
‘-o file-name’ : Realization output file (default: ‘RESULT_realization.txt’)
‘-no file-name’ : Neato-format output file (default: ‘RESULT_neato_format.txt’)
File-name may include an absolute path that was created in advance.

Download:
We supply the GREAL software for Windows, Linux and SunOS. 
Save the correct version according to the environment you are using.
To unzip the windows version use standard WinZip for windows.
To unzip the SunOs (Linux) version use:
gzip -d grealSun.tar.gz (grealLinux.tar.gz).
tar xvf grealSun.tar (grealLinux.tar).
After extracting you will find two files in the package: and executable file 
and an example file. The example file is "hypergraph.txt"; it can be used 
to observe the input and output formats of GREAL; and as a template for your
own hypergraphs. The executable files are described next.

Run:
GREAL was compiled on Windows, Linux and SunOS. The names of the executables are: 
Windows: GREAL.exe, Linux: grealLinux, SunOS: grealSun. 
GREAL is run from command line. You may supply 0-3 of the parameters that are described above. 
Examples on Windows are:
1. GREAL.exe
2. GREAL.exe –i my_hypergraph.txt
3. GREAL.exe –i my_hypergraph.txt –o my_result_realization.txt

Neato:
Graphviz is an open source graph drawing software, which can be downloaded at 
http://www.research.att.com/sw/tools/graphviz/. This package contains a program called neato 
which can be used to visualize the GREAL solution. After a successful run of GREAL, run neato on 
the file RESULT_neato_format.txt is produced.