说明：  在实际系统中，或者因为不易直接测量，或者因为测量设备在经济性和使用性上的限制，进行状态反馈往往很困难。解决上述问题的基本途径就是进行状态重构，即设计状态观测器，利用重构状态取代真实状态进行状态反馈。
(In a real system, or because difficult to directly measure, or because the measurement device is limited to economic and usability on the state feedback is often very difficult. The basic way to solve these problems is to reconstruct the state, that state observer design, the use of the reconstruction replace the true state of the state status feedback.)