How to use decoding of binary LDPC as in Elec. Letters by MacKay&Neal 13March1997

Hello, I want need to exploit "LDPC as in Elec. Letters by MacKay&Neal 13March1997" which wrote by Igor Kozintsev.

        SNR=[-10:5];
        for i=1:length(SNR)
        sigma = 10^((-SNR(i))/20);                          % AWGN noise deviation
        x = (sign(randn(1,size(G,1)))+1)/2; % random bits
        y = mod(x*G,2);                     % encoding

        z = 2*y-1;                          % BPSK modulation
        z=z + sigma*randn(1,size(G,2));     % AWGN transmission

        f1=1./(1+exp(-2*z/sigma^2));        % likelihoods
        f1 = (f1(:))';                      % make it a row vector
        f0=1-f1;
        [z_hat, success, k] = ldpc_decode_LR(y,f0,f1,H);
        x_hat = z_hat(size(G,2)+1-size(G,1):size(G,2));
        x_hat = x_hat'; 
        Error(i)=length(find(x-x_hat))
        end

But I have a problem to create G and H matrixes. is there any suggestion how I can create G and H matrixes. Now I have predefined matrixes which I extracting from this code: https://www.mathworks.com/matlabcentral/fileexchange/28437-simulating-2-2-mimo-ldpc-base-band-systems