>> n=1

n =
     1

>> p=1

p =
     1

>> G_par1=(n-0.05)/(n+0.05)/(s+1.25*(n-0.05)/(n+0.05))/(s+12.5*(n-0.05)/(n+0.05))/(s+p)^2

G_par1 =
                     0.9048
  ---------------------------------------------
  s^4 + 14.44 s^3 + 38.67 s^2 + 38.02 s + 12.79
 
Continuous-time transfer function.

>> figure(1)
>> rlocus(G_par1)
>> p_par1=pole(G_par1)

p_par1 =

 -11.3095 + 0.0000i
  -1.1310 + 0.0000i
  -1.0000 + 0.0000i
  -1.0000 - 0.0000i

>> G_par1_zpk=zpk(G_par1)

G_par1_zpk =
 
            0.90476
  ---------------------------
  (s+11.31) (s+1.131) (s+1)^2
 
Continuous-time zero/pole/gain model.

>> figure(2)
>> nyquist(G_par1)

====================================================================================
>> p=-1

p =
    -1

>> G_par1_meno1=(n-0.05)/(n+0.05)/(s+1.25*(n-0.05)/(n+0.05))/(s+12.5*(n-0.05)/(n+0.05))/(s+p)^2

G_par1_meno1 =
                     0.9048
  ---------------------------------------------
  s^4 + 10.44 s^3 - 11.09 s^2 - 13.14 s + 12.79
 
Continuous-time transfer function.

>> p_par_meno1=pole(G_par1_meno1)

p_par_meno1 =

 -11.3095 + 0.0000i
  -1.1310 + 0.0000i
   1.0000 + 0.0000i
   1.0000 - 0.0000i

>> figure(5)
>> nyquist(G_par1_meno1)
>> N=0

N =
     0

>> P=2

P =
     2

>> Z=N+P

Z =
     2

====================================================================================
>> p=0

p =
     0

>> G_par0=(n-0.05)/(n+0.05)/(s+1.25*(n-0.05)/(n+0.05))/(s+12.5*(n-0.05)/(n+0.05))/(s+p)^2

G_par0 =
            0.9048
  ---------------------------
  s^4 + 12.44 s^3 + 12.79 s^2
 
Continuous-time transfer function.

>> G_par0_zpk=zpk(G_par0)

G_par0_zpk =

          0.90476
  -----------------------
  s^2 (s+11.31) (s+1.131)
 
Continuous-time zero/pole/gain model.

>> figure(2)
>> nyquist(G_par0)