How can I generate a gaussian distribution of spheres in a cylinder? Spheres doesn't have to overlap. Thanks

 %check for overlapping
    k=1; %start overlap check from the beginning
    while k<=i
        %take coordinates of k-th sphere
        Xk=x1(1,k);
        Yk=y1(1,k);
        Zk=z1(1,k);
        Rk=r(1,k);
        %distance between i-th and k-th sphere centers
        d(k) =sqrt((X-Xk)^2+(Y-Yk)^2+(Z-Zk)^2); 
        %sum of i-th and k-th sphere radii
        rr(k)=Rk+R; 
        if d(k) == 0 % exclude itself
            break;
        elseif d(k) < rr(k) %overlap condition
            %generate new coordinate for the i-th sphere
            x1(1,i)=x_lo+(x_hi-x_lo)*rand;
            y1(1,i)=y_lo+(y_hi-y_lo)*rand;
            z1(1,i)=z_lo+(z_hi-z_lo)*rand;
            r(i)= random('exp',0.8);
            X=x1(1,i);
            Y=y1(1,i);
            Z=z1(1,i);
            R=r(1,i);
            k=1; %reset overlap check to the beginning
            continue;
        else 
            k=k+1; %continue overlap check for next k-th sphere
            continue;
        end
    end

[AS]

What is x_hi and x_lo?

[José-Luis]

What's a gaussian distribution of spheres?