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function [zpz,npz] = sztr_(zs,ns,tae)
%  SZTR_
%  function [zpz,npz] = sztr_(zs,ns,tae)
%  AUFGABE: bestimmung der z - transformierten fz(z) zu fs(s)
%  kontinuierliches system  : fs(s)= zs(s)/ns(s)
%  tae abtastzeit
%  diskretes system : fz(z)= zpz(z)/npz(z)
%
%  AUFRUFARTEN :
%  [zpz,npz] = sztr_ : zs = zps_ , ns = nps_  , tae = ta_
%  [zpz,npz] = sztr_(zs,ns) : tae = ta_
%  [zpz,npz] = sztr_(zs,ns,tae)



if nargin == 0
   zs = zps_ ;
   ns = nps_ ;
   tae = ta_  ;
end
if nargin == 2
   tae = ta_;
end
[ac,bc,cc,dc] = tf2ss(zs,ns);
[ad,bd] = c2d(ac,bc,tae);
[zpz,npz] = ss2tf(ad,bd,cc,dc,1);
 

% ZQTR_
% function [zpq,npq] = zqtr_(zpz,npz,ta)
% AUFGABE: bestimmung von  fq(q) zu  fz(z) ( fz(z) -> fq(q) )
% fz(z) = zpz(z)/npz(z)
% fq(q) = zpq(q)/npq(q)
% ta ... Abtastzeit
%
% AUFRUFARTEN : bezueglich der eingaenge
% zqtr_(zpz,npz,ta)
% zqtr_(zpz,npz) ; ta = ta_ ( globale groesse )
Gq = zeros(1,(length(w)));
Absq = zeros(1,(length(w)));
Phiq = zeros(1,(length(w)));
zpz=num;
npz=den;


[az,bz,cz,dz] = tf2ss(zpz,npz);
[aq,bq,cq,dq] = bilin(az,bz,cz,dz,-1,'Tustin',ta);
[zpq,npq] = ss2tf(aq,bq,cq,dq,1);

for i=1:1:length(w)
  ome=(2/ta)*tan(2*pi*w(i)*(ta/2));
  numq=zpq;
  denq=npq;
  Gq=tf(numq,denq);
  Absq(i)=Abs(Gq(i));
  Phiq(i)=angle(Gq(i))*360/(2*pi);
end
subplot(2,1,2);
plot(w, Absq);
subplot(2,1,2);
plot(w, Phiq);