so i made a state space model of a physical system where A matrix is 4 by 4 and B matrix is 4 by 1. I have 2 inputs in the system and 1 output. I used Matlab to create the A,B,C,D matrices and i used the ctrb (controlability matrix), then the rank function. instead of rank 4 (full rank) i get rank 3. from my understanding this means my system is not fully observable. does this mean i cannot create a state space feedback with the equations and would have to go with something like fuzzy logic or PID for a feedback?