In a simple case of a mass spring damper mx''+cx'+kx=F
convert system equations to a transfer function
m=1;c=1;k=1; %replace with your own values
plant=1/(m*s^2+c*s+k);
Now define a controller
C=5; %simple proportinal gain
C=pid(5,1); % PI compensator
Compute closed loop transfer function and plot step response:
CL=feedback(C*plant,1);
step(CL);
HTH.
