中文说明：
该程序构造了列权4围8的准循环LDPC码，给定k（行权），j（列权）固定为4，m（每个子矩阵的大小）。程序首先构造一个距离图，然后将其转换为矩阵。
English Description：
This program constructs coumn-weight four girth 8 quasi-cyclic LDPC codes given k (row weight), j(column weight) is fixed at 4 and m (size of each sub-matrix). The program constructs a distance graph first then converts it into a matrix.