i have a problem ..help me

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);

[belal hariz belgacem]

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

[Renato SL]

from my experience with these functions, you don't need to declare the variables symbolically (no need for the line syms f j k k1 , etc) & you only need to assign the numeric values for all of the variables.

[Walter Roberson]

The Control System Toolbox does not support any symbolic parameters, for anything. There are some things that it support "tunable" parameters for, but at any given time a tunable parameter has a specific value.