Zeros, poles and gain

You may also enter the system as poles, zeros and gain. For example:

Given a system with double zeros located at -1 and 1, and double poles located at $j$ and $-j$

>>  z=[-1;-1;1;1]

z =

    -1
    -1
     1
     1

>> p=[-j;-j;j;j]

p =

        0 - 1.0000i
        0 - 1.0000i
        0 + 1.0000i
        0 + 1.0000i

>> k=0.5

k =

    0.5000

>> sys=zpk(z,p,k,-1)
 
Zero/pole/gain:
0.5 (z+1)^2 (z-1)^2
-------------------
   (z^2  + 1)^2
 
Sampling time: unspecified