function [magout,phase,w] = dbode(a,b,c,d,Ts,iu,w)
%DBODE  Bode frequency response for discrete-time linear systems.
%   DBODE(A,B,C,D,Ts,IU) produces a Bode plot from the single input IU
%   to all the outputs of the discrete state-space system (A,B,C,D).
%   IU is an index into the inputs of the system and specifies which
%   input to use for the Bode response.  Ts is the sample period.  
%   The frequency range and number of points are chosen automatically.
%
%   DBODE(NUM,DEN,Ts) produces the Bode plot for the polynomial 
%   transfer function G(z) = NUM(z)/DEN(z) where NUM and DEN contain
%   the polynomial coefficients in descending powers of z. 
%
%   DBODE(A,B,C,D,Ts,IU,W) or DBODE(NUM,DEN,Ts,W) uses the user-
%   supplied freq. vector W which must contain the frequencies, in 
%   radians/sec, at which the Bode response is to be evaluated.  
%   Aliasing will occur at frequencies greater than the Nyquist 
%   frequency (pi/Ts).  See LOGSPACE to generate log. spaced frequency
%   vectors.  With left hand arguments,
%       [MAG,PHASE,W] = DBODE(A,B,C,D,Ts,...)
%       [MAG,PHASE,W] = DBODE(NUM,DEN,Ts,...) 
%   returns the frequency vector W and matrices MAG and PHASE (in 
%   degrees) with as many columns as outputs and length(W) rows.  No 
%   plot is drawn on the screen. 
%
%   See also:  BODE, LOGSPACE, SEMILOGX, MARGIN, NICHOLS, and NYQUIST.

%   J.N. Little 10-11-85
%   Revised Andy Grace 8-15-89 2-4-91 6-20-92
%   Revised Clay M. Thompson 7-10-90
%   Revised A.Potvin 10-1-94
%   Copyright (c) 1986-1999 The Mathworks, Inc. All Rights Reserved.
%   $Revision: 1.9 $  $Date: 1999/01/05 15:21:49 $

ni = nargin;
no = nargout;
if ni==0,
   eval('dexresp(''dbode'')')
   return
end
error(nargchk(3,7,ni));

% Determine which syntax is being used
switch ni
case 3
   if size(a,1)>1,
      % SIMO syntax
      a = num2cell(a,2);
      den = b;
      b = cell(size(a,1),1);
      b(:) = {den};
   end
   sys = tf(a,b,c);
   w = [];

case 4
   % Transfer function form with time vector
   if size(a,1)>1,
      % SIMO syntax
      a = num2cell(a,2);
      den = b;
      b = cell(size(a,1),1);
      b(:) = {den};
   end
   sys = tf(a,b,c);
   w = d;

case 5
   % State space system without iu or time vector
   sys = ss(a,b,c,d,Ts);
   w = [];

otherwise
   % State space system, with iu but w/o time vector
   if min(size(iu))>1,
      error('IU must be a vector.');
   elseif isempty(iu),
      iu = 1:size(d,2);
   end
   sys = ss(a,b(:,iu),c,d(:,iu),Ts);
   if ni<7,
      w = [];
   end
end

if no==0,
   bode(sys,w);
else
   [magout,phase,w] = bode(sys,w);
   [Ny,Nu,lw] = size(magout);
   magout = reshape(magout,[Ny*Nu lw]).';
   phase = reshape(phase,[Ny*Nu lw]).';
end

% end dbode
