n=[0:1:9];
x=cos(0.48*pi*n)+cos(0.52*pi*n);
X=fft(x);
magx=abs(X(1:1:10));
k=0:1:9;
w=2*pi/10*k;
subplot(3,1,1);
stem(w/pi,magx);
title('N=10點DFT幅度');
xlabel('頻率(單位:pi)');
axis([0,1,0,10]);
n=[0:1:9];
y=cos(0.48*pi*n)+cos(0.52*pi*n);
n1=[0:1:99];
x=[y(1:1:10) zeros(1,90)];
x1=fft(x);
magx1=abs(x1(1:1:50));
k1=0:1:49;
w1=2*pi/100*k1;
subplot(3,1,2);
stem(w1/pi,magx1);
title('補零到一百點DFT幅度');
xlabel('頻率(單位:pi)');
axis([0,1,0,10]);
n=[0:1:99];
x=cos(0.48*pi*n)+cos(0.52*pi*n);
X=fft(x);
magx=abs(X(1:1:50));
k=0:1:49;
w=2*pi/100*k;
subplot(3,1,3);
stem(w/pi,magx);
title('N=100點DFT幅度');
xlabel('頻率(單位:pi)');
axis([0,1,0,60]);