I want get matrix

matrix_FA=zeros(SSf,SSa);
Ln_total=0;
while Ln_total<round(C0*SSf*SSa)
    Type=randi(2);   %,1:P->A; 2:A->P
    if Type==1
        if rand<=P_N
            f_si=randsrc(1,1,[1:SSf;F_site/sum(F_site)]);
        else
            f_si=randsrc(1,1,[1:SSf;1/SSf*ones(1,SSf)]);
        end
        si_part=ceil(4*f_si/SSf);
        
        if rand<=P_Q  
            
            
            A_rang=1+(si_part-1)*SSa/4:si_part*SSa/4;
            A_dens=A_site(1+(si_part-1)*SSa/4:si_part*SSa/4);
        else
            A_rang=1:SSa;
            A_dens=A_site;
        end
        if rand<=P_N
            a_si=randsrc(1,1,[A_rang;A_dens/sum(A_dens)]);
        else
            a_si=randsrc(1,1,[A_rang;1/length(A_rang)*ones(1,length(A_rang))]);
        end

please help me how they create this matrix

[Walter Roberson]

You initialize matrix_FA but you never store anything into it?

You calculate several variables but you do not take copies of them each iteration, so the final result stored in them is going to be whatever was stored in the last iteration.