This function checks whether a SISO state space system is detectable or not.
A system is detectable for the continuous-time case if all of the unobservable eigenvalues have neagtive real part or for the discrete-time case if all of the unobservable eigenvalues are in the complex unit circle respectively. Hence, a oberservable system is always detectable of course.
As observability is a dual concept of controllability, the concept of detectability is dual to stabilizability, that is, a system is detectable if the pair (A', C') is stabilizable. Therefore, the same algorithm to check stabilizability are applied to the dual pair (A', C') of the system:
To check stabilizability (see Modelica_LinearSystems2.StateSpace.Analysis.isStabilizable) , ths system is transformed to to upper controller Hessenberg form
| * * ... ... * | | * | | * * ... ... * | | 0 | Q*A*Q ' = H = | 0 * ... ... * |, Q*b = q = | . |, c*Q = ( *, ..., * ) | . . . . . | | . | | 0 ... 0 * * | | 0 |
The system can be partitioned to
H=[H11,H12; H21, H22], q=[q1;0],
where the pair (H11, q1) contains the controllable part of the system, that is, rank(H) = rank(H11). For stabilizability the H22 has to be stable.
encapsulated function isDetectableSISO import Modelica; import Modelica_LinearSystems2; import Modelica_LinearSystems2.StateSpace; import Modelica_LinearSystems2.Math.Complex; input StateSpace ss "State space system"; output Boolean detectable; end isDetectableSISO;