A = 1;
M = 4;
N = 64;

k = [0:(M-1)];
x=[ones(1,M) zeros(1,N-M)];
figure;
subplot(311)
plot(x, '.', 'MarkerSize', 12)
xlabel('\itn')
ylabel('\itx{(\itn)}')

[X,Ax,phix]=fnDFT(x);

subplot(312)
plot((0:N-1),Ax)
subplot(313)
plot((0:N-1),phix)