R=0.02;t=-2:R:2;
f=Heaviside(t+1)-Heaviside(t-1)
W1=2*pi*5;
N=500;k=0:N;W=k*W1/N;
F=f*exp(-j*t'*W)*R;
F=real(F);
W=[-fliplr(W),W(2:501)];
F=[fliplr(F),F(2:501)];
subplot(2,1,1);
plot(t,f);
xlabel('t');
ylabel('f(t)');
title('f(t)=u(t+1)-u(t-1)')
subplot(2,1,2);
plot(W,F);
xlabel('w');
ylabel('f(t)的傅里葉變換F(w)');