Why my - tf2sym - command is not working?

Hello, i am trying to do my homework but my tf2sym command is not working.

İt says "Unrecognized function or variable 'tf2sym'."

What can i do about it?

I looked to add-ons and i have all toolboxes currently, it shows. Please can someone help me?

Gs=tf(1,[1 10 27 18]);
Gss= tf2sym(Gs)

Answer 1

[Sam Chak]

Hi @Enes Emre Öztürk,

I guess you want to convert the transfer function to state-space nodel.

Gs  = tf(1, [1 10 27 18])

Gs =
 
             1
  ------------------------
  s^3 + 10 s^2 + 27 s + 18
 
Continuous-time transfer function.

%% Method 1: Using tf2ssm() 
[A, B, C, D] = tf2ssm(1, [1 10 27 18])

A = 3×3

-10 -27 -18 1 0 0 0 1 0

B = 3×1

1 0 0

C = 1×3

0 0 1

D = 0

%% Method 2: Directly using ss() function
Gss = ss(Gs)

Gss =
 
  A = 
          x1     x2     x3
   x1    -10  -6.75  -2.25
   x2      4      0      0
   x3      0      2      0
 
  B = 
         u1
   x1  0.25
   x2     0
   x3     0
 
  C = 
        x1   x2   x3
   y1    0    0  0.5
 
  D = 
       u1
   y1   0
 
Continuous-time state-space model.

Answer 2

[Star Strider]

If you want to conovert that transfer function to a symbolic variable, try this —

Gs=tf(1,[1 10 27 18]);
Gss= tf2sym(Gs)

Gss = 

whos Gss

  Name      Size            Bytes  Class    Attributes

  Gss       1x1                 8  sym                

function symtf = tf2sym(sys)
TF = tf(sys);
n = TF.Numerator;
d = TF.Denominator;
s = sym('s');
symtf = poly2sym(n,s) / poly2sym(d,s);
end

I can find no reference to any function called ‘tf2sym’ so I created one.

.