Abstract
In this paper, the relation between identifiability and controllability is described and the method of determining model order is stated.
The determinant of a controllability matrix is thought to be the index of the degree of identifiability, that is, the system with small value of this determinant is considered difficult to identify.
Two cases are considered to diminish the determinant: 1) In the case the distance between the poles and zeroes of the transfer function are small and 2) the system gain is small.
In the first case, the system is considered to be essentially difficult to identify, but in the 2nd case, the system order can be determined by the ratio of the determinant.
By computer simulation, the results stated above are shown.