Find below a simple example;
A = rand(3); % random system A matrix
B = rand(3,2); % random input B matrix
C = eye(3); % state feedback
sys = ss(A,B,C,D); % open loop system x_dot = Ax+Bu
% y = Cx
K = lqr(sys,eye(3)*1e5,eye(2)); % simple controller via LQR method, u = -Kx
sysCL = feedback(sys*K,eye(3)); % closed loop system from 3 state reference to 3 state output
In the future, be more specific on which part you are struggling with and what you have done so far, inwhich case the answers would be a lot more beneficial for you.
