giving state-space equation from transfer function G(s)

we have transfer function G(s) as follow :

http://up.liz.ir/files/Gs.png

i want to give state-space equation from G(s). i search about it and found that is ss order that do it, and i writem-file as follow , but matlab say :"Empty state-space model"

    H = [tf([2],[1 4 1])];
    ss(H);
    ss(1);
    ss(2);

Answer 1

[Thomas]

>>  H = [tf([2],[1 4 1])]

H =

          2
    -------------
    s^2 + 4 s + 1

Continuous-time transfer function.

>> ss(H)

ans =

    a = 
         x1  x2
     x1  -4  -1
     x2   1   0

    b = 
         u1
     x1   2
     x2   0

    c = 
         x1  x2
     y1   0   1

    d = 
         u1
     y1   0

Continuous-time state-space model.

>> ss(1)

ans =

    d = 
         u1
     y1   1

Static gain.

>> ss(2)

ans =

    d = 
         u1
     y1   2

Static gain.

where are you getting the error? What version of Matlab are you on?

Answer 2

[behnam]

please help me