How to update old matlab code sel and pck

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I am working on something related with control and I tried to use complex model equation developed by an old matlab version. The resource uses 'sel' and 'pck' code. I believe the 'pck' code is the same as the 'ss' code for state space representation of systems. What does the 'sel' do in this code below? Here this is just part of the code, I have corrected the others

SS_hi = ss(A_hi,B_hi,C_hi,D_hi);
SS_lo = ss(A_lo,B_lo,C_lo,D_lo);
%% Make MATLAB matrix
%%
mat_hi = [A_hi B_hi; C_hi D_hi];
mat_lo = [A_lo B_lo; C_lo D_lo];
%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%% Longitudal Directional %%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%% Select the components that make up the longitude A matrix
%%
A_longitude_hi = sel(mat_hi,[3 5 7 8 11 13 14], [3 5 7 8 11 13 14]);
A_longitude_lo = sel(mat_lo,[3 5 7 8 11 13 14], [3 5 7 8 11 13 14]);
%% Select the components that make up the longitude B matrix
%%
B_longitude_hi = sel(mat_hi,[3 5 7 8 11 13 14], [19 20]);
B_longitude_lo = sel(mat_lo,[3 5 7 8 11 13 14], [19 20]);
%% Select the components that make up the longitude C matrix
%%
C_longitude_hi = sel(mat_hi,[21 23 25 26 29], [3 5 7 8 11 13 14]);
C_longitude_lo = sel(mat_lo,[21 23 25 26 29], [3 5 7 8 11 13 14]);
%% Select the components that make up the longitude D matrix
%%
D_longitude_hi = sel(mat_hi,[21 23 25 26 29], [19 20]);
D_longitude_lo = sel(mat_lo,[21 23 25 26 29], [19 20]);
SS_long_hi = ss(A_longitude_hi, B_longitude_hi, C_longitude_hi, D_longitude_hi);
SS_long_lo = ss(A_longitude_lo, B_longitude_lo, C_longitude_lo, D_longitude_lo);
%%%%%%%%%%%%%%%%%%%%%%%%%%%
%% Lateral Directional %%%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%
%% Select the components that make up the lateral A matrix
%%
A_lateral_hi = sel(mat_hi,[4 6 7 9 10 12 13 15 16], [4 6 7 9 10 12 13 15 16]);
A_lateral_lo = sel(mat_lo,[4 6 7 9 10 12 13 15 16], [4 6 7 9 10 12 13 15 16]);
%% Select the components that make up the lateral B matrix
%%
B_lateral_hi = sel(mat_hi,[4 6 7 9 10 12 13 15 16], [19 21 22]);
B_lateral_lo = sel(mat_lo,[4 6 7 9 10 12 13 15 16], [19 21 22]);
%% Select the components that make up the lateral C matrix
%%
C_lateral_hi = sel(mat_hi,[22 24 25 27 28 30], [4 6 7 9 10 12 13 15 16]);
C_lateral_lo = sel(mat_lo,[22 24 25 27 28 30], [4 6 7 9 10 12 13 15 16]);
%% Select the components that make up the lateral D matrix
%%
D_lateral_hi = sel(mat_hi,[22 24 25 27 28 30], [19 21 22]);
D_lateral_lo = sel(mat_lo,[22 24 25 27 28 30], [19 21 22]);
SS_lat_hi = ss(A_lateral_hi, B_lateral_hi, C_lateral_hi, D_lateral_hi);
SS_lat_lo = ss(A_lateral_lo, B_lateral_lo, C_lateral_lo, D_lateral_lo);
%% Make longitudal direction SYSTEM matrix
%%
sys_long_hi = pck(A_longitude_hi, B_longitude_hi, C_longitude_hi, D_longitude_hi);
sys_long_lo = pck(A_longitude_lo, B_longitude_lo, C_longitude_lo, D_longitude_lo);