state space into transformer function ......where is the problem

clear all, close all, clc;

syms f j k1 k R l

%% State space representation

A = [-f/j k1/j;(-k-k1)/l -R/l];

% the state matrix

B = [0 -1/j;k/j 0];

% the input vector

C = [1 0;0 1];

% the output vector

D = zeros(size(C,2),size(B,2));

% the feedforward

%% Verify the controllability and observability

Mc = ctrb(A,B);

% Controllability matrix

Om = obsv(A,C)

% matrix

the_means_not_controllable = length(A)-length(Mc)

if rank(Mc) == size(A,2)

'It is controllable'

else

'It is not controllable'

end

if rank(Om) == size(A,2)

'It is observable'

else

'It is not observable'

end

%% Transform into transfer function

[num,den] = ss2tf(A,B,C,D)

sys = tf(num,den)

%Order system

Order_system = order(sys)

step(sys,'g')

grid on

.................................................................the problem

Error using ctrb (line 20)

The "ctrb" command cannot be used for models of class "sym".

Error in state_space (line 19)

Mc = ctrb(A,B);