When an LTI system is NOT completely controllable/observable, does the linear differential equation governing the system give the internal or the external description of a system?


External. That's the whole point: The behavior of any LTI system can be completely characterized by it's transfer function, impulse response, differential equation, etc. (which can all be converted into each other).

That's a "black box" description and gives no information on the internal details of the system. There many different physical realizations of the same system, but you can't tell from just the outside behavior

  • $\begingroup$ So can there be "hidden" characteristic modes of the system which the diff eqn doesn't tell us about..? $\endgroup$ – nn08 Aug 23 '19 at 13:23
  • $\begingroup$ And just one more bit.. The impulse response of the whole system.. Is it a linear combination of ALL the characteristic modes given by the diff eqn only..? $\endgroup$ – nn08 Aug 23 '19 at 13:27

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