Square wave fourier

% square wave
clear
clc
k_max = input('Enter>>');
num_kmax = length(k_max);
for z = 1:num_kmax
    k = [-k_max(z):k_max(z)];
    L_k = length(k);
    a_k = zeros(1, L_k); % Form vector of Fourierseries coefficients,

    for i=1:2:L_k % as a zero array and then
        if mod(abs(k(i)),4)==1
            a_k(i)=2/(pi*abs(k(i)));

        else if mod(abs(k(i)),4)==3
            a_k(i)=-2/(pi*abs(k(i)));
            end
        end
    end

    omega_0 = 2*pi;
    t = 0:.005:3;
    x = a_k*exp(j*omega_0*k'*t);

    subplot(num_kmax,1,z),plot(t,real(x)), ylabel('partialsum'),...
    axis([0 3 -1.5 1.5]), text(.05,-.25,['max. har. =',num2str(k_max(z))]),...
    text(2.0,-.25,['Name / Matric No']),
end
xlabel('t');