%==========================================================================
%  Name：fre_fir.m
%  The program compute the DTFT of discrete-time sequence x(n),
%  and plot the curves.
%==========================================================================
clear;close all;
h=input('Type in the impulse response h(n)=');
N=length(h);

w=0:0.1:2*pi;Hg1=0;
for i=0:N-1
    m=-N/2+i-0.5;
    Hg=h(i+1)*cos((i-(N-1)/2)*w);
    Hg1=Hg1+h(i+1)*cos((i-(N-1)/2)*w);
end

n=0:N-1;               

subplot(2,1,1);stem(n,h,'.');grid on;
xlabel('Index n');ylabel('the curve of h(n)');
title('The frequence response of the filter h(n)');
subplot(2,1,2);plot(w/(pi),Hg1);grid on;axis([0,2,min(Hg1),max(Hg1)])
xlabel('w');