Problem using zpkdata function.

Problem arises when i want to do the calculation of the transfer function gain using this code inside the For loop, for each h2 analyzed.

sp ='the dc gain is %f and the gain of the tf is %f';
for i = 1:length(z)
    zc = z(i);
    %graph2
    num2 = 5 / zc * [1 zc]; % [] valor de los coeficientes del numerador de H(S)
    h2   = tf(num2, dem)
    dc = dcgain(h2);
    [z,p,k] = zpkdata(h2);
    k
    fprintf(sp,dc,k)
end

[Shanmukha Voggu]

Please provide the information about the dem variable in your code?