function out_bits = extract(r, g, L);
%     this function is to extract the info bit from the code bit under L 
% parallel encoders. L is the number of inner encoders.
%     for the woven encoder all use systemetic coding, 
% we can extract the outer decoder's input bits from the source of inner decoder.
        
    global sim_consts;
    
    len = length(r);
    
    pcode = zeros(sim_consts.Li, fix(len/sim_consts.Li));
    ucode = zeros(sim_consts.Li, fix(len/sim_consts.Li)*sim_consts.Ri);
    out_bits = zeros(1, fix(len*sim_consts.Ri) - sim_consts.Li*sim_consts.mi*sim_consts.enci.k);
    
    pcode = reshape(r, sim_consts.Li, fix(len/sim_consts.Li));    
    for i = 1:sim_consts.Li        
        for j = 1:(len/sim_consts.Li)/sim_consts.enci.n - sim_consts.mi
            ucode(i, (j-1)*sim_consts.enci.k+1 : j*sim_consts.enci.k ) = pcode(i, (j-1)*sim_consts.enci.n+1 : (j-1)*sim_consts.enci.n+sim_consts.enci.k);
        end
    end
    
    out_bits = reshape(ucode, 1, len*sim_consts.Ri);
return;