LQR Command Failure: Troubleshooting and Solutions

The 'lqr' command failed to stabilize the plant or find an optimal feedback gain. To remedy this problem:

1. Make sure that all unstable poles of A are controllable through B (use MINREAL to check). If there are uncontrollable unstable poles, the system needs to be redesigned or a controller added to achieve controllability.
2. Modify the weights Q and R to make [Q N;N' R] positive definite (use EIG to check positivity). If the weight matrices are not positive definite, the LQR control design requires selecting appropriate weights.