x=[1,2,3,4,5,6,6,5,4,3,2,1];w=[0:1:500]*2*pi/500;
[H]=freqz(x,1,w);
magH=abs(H);phaH=angle(H);
subplot(2,2,1);plot(w/pi,magH);grid
axis([0,2,0,50]);
xlabel('');ylabel('|x|');title('DTFT的幅度')
subplot(2,2,2);plot(w/pi,phaH/pi*180);grid
axis([0,2,-400,400]);
xlabel('以pi為單位的頻率');ylabel('度');title('DTFT的相角')

N=12;w1=2*pi/N;k=0:N-1;
x=[1,2,3,4,5,6,6,5,4,3,2,1];
X=dft(x,N);
magX=abs(X),phaX=angle(X)*180/pi
subplot(2,2,3);plot(w*N/(2*pi),magH,'--');
axis([-0.1,12.1,0,50]);
hold on
stem(k,magX);
ylabel('|x(k)|');title('DFT的幅度:N=12');
hold off
subplot(2,2,4);plot(w*N/(2*pi),phaH*180/pi,'--');
axis([-0.1,12.1,-400,400]);
hold on
stem(k,phaX);
ylabel('度');title('DFT的相角:N=12');