A state-space model is said to be observable if, for any initial time, the state vector can be determined from the outputs of the model, measured over a finite time.
accepts a Method option. The following settings can be specified:
"Matrix"
tests if the observability matrix has full rank
"Gramian"
tests if the observability Gramian is positive definite
"PBH"
uses the Popov-Belevitch-Hautus rank test
With the default setting Method->Automatic, each method is evaluated in turn until the system is determined to be observable or all methods have been exhausted.