On discrete algebraic Riccati equations: A rank characterization of solutions

Athalye, Sanand;Pillai, Harish K.;Jungers, Raphaël
(2017) Linear Algebra and Its Applications — Vol. 527, p. 184-215 (2017)

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Authors
  • Athalye, SanandUCLouvain
    Author
  • Pillai, Harish K.IIT Bombay, Powai, India
    Author
  • Author
Abstract
We give a rank characterization of the solution set of discrete algebraic Riccati equations (DAREs) involving real matrices. Our characterization involves the use of invariant subspaces of the system matrix. We observe that a DARE can be considered as a specific type of a non-symmetric continuous-time algebraic Riccati equation. We show how to extract the low rank solutions from the full rank solution of a homogeneous DARE. We also study the eigen-structure of various feedback/closed loop matrices associated with solutions of a DARE. We show as a consequence of our observations that a solution X of a DARE for controllable systems and certain specific types of uncontrollable systems satisfies the inequality Xmin≤X≤Xmax. We characterize conditions under which the solution set of DARE is bounded/unbounded. We use the method of invariant subspaces to identify some invariant sets of a difference Riccati equation.
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Citations

Athalye, S., Pillai, H. K., & Jungers, R. (2017). On discrete algebraic Riccati equations: A rank characterization of solutions. Linear Algebra and Its Applications, 527, 184-215. https://doi.org/10.1016/j.laa.2017.04.001 (Original work published 2017)