n=0:99;
xn=2*sin(4*pi*n)+5*cos(8*pi*n);
                                      %生成信號序列
Xk=fft(xn);
kx=0:length(Xk)-1;
subplot(2,1,1);
stem(n,xn);
title('time domain signal');
                                      %繪制源曲線信號
subplot(2,1,2);
stem(kx,abs(Xk));           
title('frequence domain signal');