%  ex_07_07_1.m :  習題 7.7

clear all;
N=31;
for i=0:N-1
    w(i+1)=abs(sin(2*pi*i/N))/pi-(1-2*abs(i-N/2)/N)*cos(2*pi*i/N);
end
[W,f]=freqz(w,1,256,'whole',1);
subplot(221);
t=0:N-1;
stem(t,w,'.k')
W=20*log10(abs(W)/abs(W(1)));
f=f-0.5;
subplot(222);
plot(f,fftshift(W));grid on;