f_pzplot.asv

digital signal processing常用工具箱

function pos = f_pzplot (b,a,caption)

%F_PZPLOT: Construct plot showing transfer function poles and zeros
%
%             H(z) = b(z)/a(z)
%
% Usage: pos = f_pzplot (b,a,caption);
%
% Descripion: Plot the poles and zeros of the linear discrete-time system
%
% On entry:   b       = vector containing numerator coefficients
%             a       = vector containing denominator coefficients
%             caption = plot title
%
% On exit:    pos = 1 by 4 position vector of pole-zero plot
%-----------------------------------------------------------------------------------

% Find poles and zeros

pole = roots(a);   
zero = roots(b);
r = length(zero) - length(pole);

if r > 0
   pole = [pole ; zeros(r,1)];
elseif r < 0
   zero = [zero ; zeros(-r,1)];
end
np = length(pole);
nz = length(zero);

% Look for pole-zero cancellation

cancel = 1;
while cancel == 1
   cancel = 0;
   for i = 1 : np
      for j = 1 : nz
         dist = abs(zero(j)-pole(i));
         if dist < 1.e-6
            cancel = 1;
            pole = [pole(1:i-1) ; pole(i+1:np)];
            np = length(pole);
            zero = [zero(1:j-1) ; zero(j+1:nz)];
            nz = length(zero);
            break;
         end
      end
      if cancel == 1
         break
      end
   end
end

% Plot poles and zeros

phi = linspace(0,2*pi,361);
x0 = cos(phi);
y0 = sin(phi);
hold off
box off
plot(x0,y0,'k',[-2 2],[0 0],'k',[0 0],[-2 2],'k')
axis square
hold on
for i = 1 : np
   plot(real(pole(i)),imag(pole(i)),'rx')
end
for i = 1 : nz
   plot(real(zero(i)),imag(zero(i)),'ro')
end
xmax = max(abs(get(gca,'Xlim')));
ymax = max(abs(get(gca,'Ylim')));
range = max(xmax,ymax);
axis([-range range -range range])
plot([-range range],[0 0],'k',[0 0],[-range range],'k')

% Labels

set (gca,'FontSize',9)
f_labels ('','Re(z)','Im(z)')
if (nargin < 3)
   f_labels ('Pole-Zero Plot','Re(z)','Im(z)')
else
   f_labels (caption,'Re(z)','Im(z)')
end
pos = get(gca,'Position');

%-----------------------------------------------------------------------------------