%  ex_07_03_1.m :  習題 7.3

clear all;
fl=pi/4; N=29;
factor=(N+1)/2;
m=factor*fl/pi;
m=floor(m);
j=sqrt(-1);
for k=0:(N-1)
    if(k<=m)||(k>=(N-m))
        a=-j*(N-1)*k*pi/N;
        H(k+1)=exp(a);
    else
        H(k+1)=0;
    end
end;
for i=0:(N-1)
    s=0;
    for k=0:(N-1)
        a=j*2*pi*i*k/N;
        s=s+H(k+1)*exp(a);
    end
    h(i+1)=s/N;
end
h=real(h); h1=freqz(h,1,N);
t=0:0.5/N:0.5-0.5/N;
figure('color','w');
subplot(221);plot(t,abs(h1));grid;