% fg_05_03  Realizable filter power gain
M=1000;
L=[4 8 128];
xa=[.083 .082 .095]; ya=[-4 -1 2];
nuc=0.1;
nu=linspace(0,.5,M);
clr=['r','b','g'];
sp_fig(1,7,5);
axis([0 .5 -40 5]);
set(gca,'fontsize',16,'position',[.12 .15 .9-.12 .9-.15]);
for n=1:length(L), 
   k=[0:L(n)-1];
   b1=sin(2*pi*nuc*(k-L(n)))./(pi*(k-L(n)));
   b=[b1,2*nuc,b1(L(n):-1:1)];
   dB=20*log10(max(abs(gain_f(b,1,nu)),1.e-2));
   line(nu,dB,'color',clr(n));
   arrow(.17,ya(n),xa(n),dB(fix(xa(n)*2*M)));
   h=text(.175,ya(n),['{L}=',int2str(L(n))]);
   set(h,'fontname','times','fontsize',16);
end
grid;
xlabel('Frequency \nu (Hz-s)');
ylabel('Power gain (dB)');