Necessary and Sufficient Conditions for Distinguishability of Linear   Control Systems
  Distinguishability takes a crucial rule in studying observability of hybrid system such as switched system. Recently, for two linear systems, Lou and Si gave a condition not only necessary but also sufficient to the distinguishability of linear systems. However, the condition is not easy enough to verify. This paper will give a new equivalent condition which is relatively easy to verify. 
Hongwei Lou
math.OC cs.SY