利用matlab建立模型，求传递函数

连续传递函数Ds用tf输入最方便，不知道为什么偏要用zpk。
频率预修正的双线性变换法需要指定截止频率，这里取了个2。

;; Ds=zpk([],[-1+sqrt(2)*i -1-sqrt(2)*i],1);
;; Dz1=zpk(c2d(Ds,1,;zoh;));
;; Dz1.Variable=;z^-1;

Zero/pole/gain:
0.22856 z^-1 (1+0.4884z^-1)
-----------------------------
(1 - 0.1147z^-1 + 0.1353z^-2)

Sampling time: 1
Overloaded functions or methods (ones with the same name in other directories)
doc ident/c2d
;; Dz2=zpk(c2d(Ds,1,;tustin;));
;; Dz2.Variable=;z^-1;

Zero/pole/gain:
0.090909 (1+z^-1)^2
-----------------------------
(1 - 0.1818z^-1 + 0.2727z^-2)

Sampling time: 1
;; Dz3=zpk(c2d(Ds,1,;matched;));
;; Dz3.Variable=;z^-1;

Zero/pole/gain:
0.1701 z^-1 (1+z^-1)
-----------------------------
(1 - 0.1147z^-1 + 0.1353z^-2)

Sampling time: 1
;; Dz4=zpk(c2d(Ds,1,;prewarp;,2));
;; Dz4.Variable=;z^-1;

Zero/pole/gain:
0.13855 (1+z^-1)^2
-----------------------------
(1 + 0.3743z^-1 + 0.2883z^-2)

Sampling time: 1