>> s = zpk('s');
>> P = 2/(0.4+s)/(s^2+2*s+1)

P =

         2
  ---------------
  (s+0.4) (s+1)^2

Continuous-time zero/pole/gain model.

>> rlocus(P)
>> [Gm,Pm,Wcg,Wcp] = margin(P);
>> [Gm,Pm,Wcg,Wcp] = margin(P)

Gm =

    1.9600


Pm =

   24.9253


Wcg =

    1.3416


Wcp =

    0.9604

>> T_krit = 2*pi/wcg
Undefined function or variable 'wcg'.

Did you mean:
>> T_krit = 2*pi/Wcg

T_krit =

    4.6832

>> K_krit = Gm

K_krit =

    1.9600

>> step(K_krit*P)
>> step(feedback(K_krit,P))
>> step(feedback(P,K_krit))
>> step(feedback(P,K_krit-1))
>>
>> step(feedback(P,K_krit-0.01))
>> step(feedback(P,K_krit-0.0000001))
>> P

P =

         2
  ---------------
  (s+0.4) (s+1)^2

Continuous-time zero/pole/gain model.

>> K_krit

K_krit =

    1.9600

>> rlocus(P)
>> test = feedback(P,K_krit)

test =

                 2
  -------------------------------
  (s+2.4) (s^2 - 5.27e-06s + 1.8)

Continuous-time zero/pole/gain model.

>> step(test)
>> step(feedback(P,K_krit))
>> step(feedback(P,K_krit-1))
>> step(feedback(P,K_krit-0.5))
>> step(feedback(P,K_krit-0.6))
>> step(feedback(P,K_krit-0.3))
>> step(feedback(P,K_krit-0.1))
>> step(feedback(P,K_krit-0.01))
>> step(feedback(P,K_krit-0.0001))
>> step(feedback(P,K_krit-0.0000001))
>> step(feedback(P,K_krit-0.00001))
>> step(feedback(P,K_krit-0.0001))
>> step(feedback(P,K_krit+0.0001))
>> step(feedback(P,K_krit+0.000001))
>> step(feedback(P*K_krit,1))
>> step(feedback(P*K_krit,1),20)
>> step(feedback(P*K_krit,1),300)
>> step(feedback(P*K_krit,1))
>> step(feedback(P*K_krit,1),2500000000000)
>> step(feedback(P*K_krit,1),2500000)
>> step(feedback(P*K_krit,1),20)
>> K_krit

K_krit =

    1.9600

>> T_krit

T_krit =

    4.6832

>> Ap=0.5*K_krit

Ap =

    0.9800

>> P_szab = pidstd(Ap,inf,0)

P_szab =

  Kp = 0.98

P-only controller.

>> P_p_szab = feedback(P_szab*P,1);
>> step(P_p_szab)
>> Ap

Ap =

    0.9800

>> Ap=0.45*K_krit;
>> Ti=0.85*T_krit;
>> Td=0;
>> PI = pidstd(Ap,Ti,0)

PI =

             1      1
  Kp * (1 + ---- * ---)
             Ti     s

  with Kp = 0.882, Ti = 3.98

Continuous-time PI controller in standard form

>> P_pi = feedback(PI*P,1)

P_pi =

                1.764 (s+0.2512)
  ---------------------------------------------
  (s+1.986) (s+0.2386) (s^2 + 0.1757s + 0.9355)

Continuous-time zero/pole/gain model.

>> step(P_pi)
>>
>>
>> P_pid = pidstd(0.6*K_krit,0.5*T_krit,0.125*T_krit)

P_pid =

             1      1
  Kp * (1 + ---- * --- + Td * s)
             Ti     s

  with Kp = 1.18, Ti = 2.34, Td = 0.585

Continuous-time PID controller in standard form

>> PID = pidstd(0.6*K_krit,0.5*T_krit,0.125*T_krit)

PID =

             1      1
  Kp * (1 + ---- * --- + Td * s)
             Ti     s

  with Kp = 1.18, Ti = 2.34, Td = 0.585

Continuous-time PID controller in standard form

>> P_pid = feedaback(PID*P,1)
Undefined function or variable 'feedaback'.

Did you mean:
>> P_pid = feedback(PID*P,1)

P_pid =

                1.3769 (s+0.8541)^2
  -----------------------------------------------
  (s^2 + 1.771s + 0.7884) (s^2 + 0.6294s + 1.274)

Continuous-time zero/pole/gain model.

>> step(P_pid)
>> P

P =

         2
  ---------------
  (s+0.4) (s+1)^2

Continuous-time zero/pole/gain model.

>> P

P =

         2
  ---------------
  (s+0.4) (s+1)^2

Continuous-time zero/pole/gain model.

>> demoAbra
>> demoAbra
>> demoAbra
>> K_krit

K_krit =

    1.9600

>> K_krit

K_krit =

    1.9600

>> demoAbra

Kp =

    1.5000


Kp =

     2


Kp =

    2.5000


Kp =

     3

Warning: Error occurred while evaluating listener
callback.
> In ctrluis.axesgroup/addlimitmgr>LocalUpdateLims (line 68)
  In wrfc.plot/draw (line 24)
  In wrfc.plot/init_listeners>LocalRedraw (line 109)
  In ctrluis.axesgroup/generic_listeners>LocalPostUnitTranform (line 232)
  In plotopts.TimePlotOptions/applyTimePlotOpts (line 19)
  In resppack.timeplot/setoptions (line 18)
  In ltiplot (line 148)
  In DynamicSystem/stepplot (line 102)
  In DynamicSystem/step (line 92)
  In demoAbra (line 9)
Operation terminated by user during
resppack.TimeFinalValueView/draw (line 20)


In wavepack.wavechar/draw (line 26)
      this.View(ct).draw(this.Data(ct),NormalRefresh);

In wavepack.waveform/draw (line 48)
      draw(c,varargin{:})

In wrfc.plot/draw (line 17)
      draw(wf)

In DynamicSystem/stepplot (line 133)
   draw(h)  % hold mode

In DynamicSystem/step (line 92)
      stepplot(varargin{:});

In demoAbra (line 9)
    step(T,20)

>> demoAbra

Kp =

    0.5000


Kp =

     1


Kp =

    1.5000


Kp =

     2

>> demoAbra

Kp =

    0.5000


Kp =

     1


Kp =

    1.5000


Kp =

     2


Kp =

    2.5000

>> demoAbra

Kp =

    1.5000


Kp =

     2


Kp =

    2.5000


Kp =

     3


Kp =

    3.5000


Kp =

     4


Kp =

    4.5000


Kp =

     5

>> P=2/(0.4+s)/(s^2+2*s+1)

P =

         2
  ---------------
  (s+0.4) (s+1)^2

Continuous-time zero/pole/gain model.

>> demoAbra

P =

         2
  ---------------
  (s+0.4) (s+1)^2

Continuous-time zero/pole/gain model.


Kp =

    1.5000


Kp =

     2


Kp =

    2.5000


Kp =

     3


Kp =

    3.5000


Kp =

     4


Kp =

    4.5000


Kp =

     5

>> demoAbra

P =

         2
  ---------------
  (s+0.4) (s+1)^2

Continuous-time zero/pole/gain model.


Kp =

    0.5000


Kp =

     1


Kp =

    1.5000


Kp =

     2


Kp =

    2.5000

>> demoAbra

P =

         2
  ---------------
  (s+0.4) (s+1)^2

Continuous-time zero/pole/gain model.


Kp =

    0.5000


Kp =

     1


Kp =

    1.5000


Kp =

     2

>> demoAbra

P =

         2
  ---------------
  (s+0.4) (s+1)^2

Continuous-time zero/pole/gain model.


Kp =

    0.5000


Kp =

     1


Kp =

    1.5000


Kp =

     2

>> demoAbra

P =

         2
  ---------------
  (s+0.4) (s+1)^2

Continuous-time zero/pole/gain model.


Kp =

    0.5000


Kp =

     1


Kp =

    1.5000


Kp =

     2

>> T_krit

T_krit =

    4.6832

>> demoAbra

P =

         2
  ---------------
  (s+0.4) (s+1)^2

Continuous-time zero/pole/gain model.


Kp =

    0.3000


Kp =

    0.6000


Kp =

    0.9000


Kp =

    1.2000

>>