%  ex_07_03_2.m :  習題 7.3

clear all;
fl=pi/6;fh=pi/3;N=29;
factor=(N+1)/2;m=factor*fl/pi;
m=floor(m);m2=factor*fh/pi;m2=ceil(m2);
j=sqrt(-1);
for k=0:(N-1)
       if((k<=m)||(k>=(N-m))||((k>=m2)&&(k<=(N-m2))))
            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;