pzplot.m

％绘制系统函数的零极点图 ％ ％pzplot(num,den) ％num为系统函数分子多项式的系数向量 ％den为系统函数分母多项式的系数向量 ％

function pzplot(num,den)
%绘制系统函数的零极点图
%
%pzplot(num,den)
%num为系统函数分子多项式的系数向量
%den为系统函数分母多项式的系数向量
%

hold on
axis('square');

%
%绘制单位元
%

x=-1:0.01:1;
y=(1-x.^2).^0.5;
y1=-(1-x.^2).^0.5;
plot(x,y,'k',x,y1,'k');

%
%求取系统的零极点
%
Lnum=length(num);
Lden=length(den);
if(Lnum>1)
    z=roots(num);
%roots多项式根    
else
    z=0;
end
if(Lden>1)
    p=roots(den);
else
    p=0;
end


%
%判断绘图范围
%
if(Lnum>1&Lden>1)
    realmaxz=max(abs(real(z)));
    imagmaxz=max(abs(imag(z)));
    axismaxz=max(realmaxz,imagmaxz);
    realmaxp=max(abs(real(p)));
    imagmaxp=max(abs(imag(p)));
    axismaxp=max(realmaxp,imagmaxp);
    axismax=max(axismaxz,axismaxp);
elseif(Lnum>1)
    realmaxz=max(abs(real(z)));
    imagmaxz=max(abs(imag(z)));
    axismax=max(realmaxz,imagmaxz);
else
    realmaxp=max(abs(real(p)));
    imagmaxp=max(abs(imag(p)));
    axismax=max(realmaxp,imagmaxp);
end

%
%确定绘图范围，并绘制出轴线和边框线
%
axis([-axismax axismax -axismax axismax]);
%axis([xmin xmax ymin ymax])自定义图形坐标尺
plot([-axismax axismax],[0 0],'k');
plot([0 0],[-axismax axismax],'k');
plot([-axismax axismax],[axismax axismax],'k');
plot([axismax axismax],[-axismax axismax],'k');
%
%绘制出零极点
%
Lz=length(z);
for i=1:Lz
    plot(real(z(i)),imag(z(i)),'ko');
end
LP=length(p);
for j=1:LP
    plot(real(p(j)),imag(p(j)),'kx');
end
title('The zeros-pole plot');
xlabel('Real');
ylabel('Imag');