A note on the downloadable parity-check matrices.
The parity-check matrices are stored either as MATLAB .mat files which are readable with MATLAB and Octave or using the .alist file format.
A thorough description of the .alist file format is given on www.inference.phy.cam.ac.uk. The first line contains the size of the matrix as columns and rows. The second line contains the maximum number of ones per column followed by the maximum number of ones per row. Then follows a line that contains, for every column of the matrix, the number of ones in this column. The next line contains, for every row of the matrix, the number of zeros in that row. The following lines contain, for each column, the positions of the ones in that column. A 0 indicates an unused entry. The following lines redundantly contain for every row the positions of the non-zero entries in that row.