The Program to test the girth 4 of Gallager LDPC codes
Copyright (C) Yang XIAO, BJTU, July 26, 2007, E-Mail: email@example.com,
The program analyzes the girth 4 for Gallager LDPC codes. The figures show
the parity check matrix H and the girth test matrix O, respectively.
Fig 1 can help us know the 1s’ distribution of the parity check matrix H.
Fig. 2 is the result of girth 4 for the given H.
Theorem in Ref : The H matrix has no gith4, if and only if the O matrix in Fig.2 has no entry value to be larger than 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
 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
 MOHAMMED ALKHANBASH, Gallager LDPC, Matlab center, File Exchange, 2007
The papers  and  can be downloaded from Web site of IEICE and IEEE Explore.