clc,clear all,close all;
n=[0:1:999];
xn=10*cos(0.2*pi*n)+1.2*cos(0.25*pi*n)+4.6*cos(0.6328*pi*n);    %先定義一個長序列，處理時再截取

%先采集128點，且加漢明窗，做DFT%%%%%%%%%%%%%%%%%%%%%%%%%
w1=hamming(128);
xn1=xn(1:128);
xn11=xn1.*w1';                 %xn11就是加了漢明窗的128點數據

%補齊0點得到256點數據，在做DFT%%%%%%%%%%%%%%%
xn2=zeros(1,128);
xn22=[xn11,xn2];
X2=fft(xn22,256);
subplot(2,1,1);
plot([0:255],X2);
xlabel('n 256-point');
ylabel('dft result --w');

%補齊0點得到512點數據%%%%%%%%%%%%%%%%%%%%%
xn3=zeros(1,384);
xn33=[xn11,xn3];
X3=fft(xn33,512);
subplot(2,1,2);
plot([0:511],X3);
xlabel('n 512-point');
ylabel('dft result --w');