Weakly coprime factorization and continuous-time systems

Helsinki University of Technology, Institute of Mathematics, PO Box 1100, FIN-02015 HUT, Finland
Email: kalle.mikkola{at}iki.fi
We give many necessary and sufficient conditions for the existence of a weakly coprime or Bézout coprime factorization of a transfer function, possibly operator valued. Some of these conditions are given in terms of the output- or state-feedback stabilizability of realizations. Our realizations are well-posed linear systems—continuous-time linear time-invariant infinite-dimensional systems. We also study further properties of such factorizations, their relations to discrete-time weakly coprime factorizations, counterexamples and (weak) left invertibility. Moreover, analogous discrete-time results are obtained. Control-theoretic consequences are indicated.
Keywords: weak coprimeness; stabilizable realization; stabilizable and detectable realization; LQ optimal state feedback; infinite-dimensional systems theory; well-posed linear systems; holomorphic fractions.