n=0:100;x=cos(pi*n/2);
k=-100:100;w=(pi/100)*k;
X=x*(exp(-j*pi/100)).^(n'*k);
y=exp(j*pi*n/4).*x;
Y=y*(exp(-j*pi/100)).^(n'*k);
subplot(2,2,1);plot(w/pi,abs(X));
xlabel('frequency');ylabel('|X|');
subplot(2,2,2);plot(w/pi,angle(X));
xlabel('frequency');ylabel('ang(X)');
subplot(2,2,3);plot(w/pi,abs(Y));
xlabel('frequency');ylabel('|Y|');
subplot(2,2,4);plot(w/pi,angle(Y));
xlabel('frequency');ylabel('ang(Y)');