function pzplotz(b,a)
%  pzplotz(b,a)  按給定系數向量b,a在z平面上畫出零極點分布圖
%  b - 分子多項式系數向量
%  a - 分母多項式系數向量
%  a,b向量可從z的最高冪降冪排至z^0,也可由z^0開始,按z^-1的升冪排至z的最負冪.
N = length(a); M = length(b); pz = []; zz = []; 
if (N > M)
     zz = zeros((N-M),1);
elseif (M > N)
     pz = zeros((M-N),1); 
end
pz = [pz;roots(a)]; zz = [zz;roots(b)];
pzr = real(pz)'; pzi = imag(pz)';
zzr = real(zz)'; zzi = imag(zz)';
rzmin = min([pzr,zzr,-1])-0.5; rzmax = max([pzr,zzr,1])+0.5;
izmin = min([pzi,zzi,-1])-0.5; izmax = max([pzi,zzi,1])+0.5;
zmin = min([rzmin,izmin]); zmax = max([rzmax,izmax]); zmm = max(abs([zmin,zmax]));
%
uc=exp(j*2*pi*[0:1:500]/500);  % 單位圓
plot(real(uc),imag(uc),'w',[-zmm,zmm],[0,0],'w',[0,0],[-zmm,zmm],'w');
axis([-zmm,zmm,-zmm,zmm]);axis('square');hold
plot(zzr,zzi,'go',pzr,pzi,'yx');hold
text(zmm*1.1,zmm*0.95,'z-平面')
xlabel('實軸');ylabel('虛軸')
title('零極點圖')