clear all
clc
close all
%實現X2(n)和X3(n)的DFT
x2n=[1,2,3,4,4,3,2,1];
x3n=[4,3,2,1,1,2,3,4];
M=[3,4];
N=2.^M; 
for i=1:2
    x2k=fft(x2n,N(i));
    subplot(2,2,i);
    stem(0:N(i)-1,abs(x2k),'.');
    grid on
    xlabel('k');
    ylabel('幅度');
    title(['\X2(k)  N=' num2str(N(i))]);
    subplot(2,2,2+i)
    stem(0:N(i)-1,angle(x2k),'.')
    grid on
    xlabel('k');
    ylabel('相位');
    title(['X2(k)  N=' num2str(N(i))]);
end