Count the number of the girth 4 of LDPC codes

The program can count the number of the girth 4 of LDPC codes.

The program can count the number of the girth 4 of LDPC codes.
Copyright (C) Yang XIAO, Jun FAN, Beijing Jiaotong University, Aug. 8,
2007, E-Mail: [e-mail].
Ref.[1] shows that it is necessary for the LDPC codes without girth 4.
The theorem about girth 4 in Ref.[1] can test the existence of girth 4, but it can not count the number of girth 4.
To solve the problem, Ref.[2] provided an algorithm of counting the number of girth 4.
This program is following the algorithm of Ref [2], and counts the number of girth 4 for Gallager LDPC codes.

Ref:
[1] Y. Xiao, M -H Lee,Low complexity MIMO-LDPC CDMA systems over multipath channels,
IEICE Transactions on Communications, v E89-B, n 5, May, 2006, p 1713-1717
[2] J. Fan, Y. Xiao, A method of counting the number of cycles in LDPC codes,
8th International Conference on Signal Processing, ICSP 2006,Volume: 3,
ISBN: 0-7803-9737-1, Digital Object Identifier: 10.1109/ICOSP.2006.345906
[3] MOHAMMED ALKHANBASH, Gallager LDPC, Matlab center, File Exchange, 2007
The papers [1] and [2] can be downloaded from Web site of IEICE and IEEE Explore,respectively.