Finite rank perturbations and solutions to the operator Riccati equation

On the existence of solutions to the operator Riccati equation and the tan Θ theorem

Let A and C be self-adjoint operators such that the spectrum of A lies in a gap of the spectrum of C and let d > 0 be the distance between the spectra of A and C . We prove that under these assumptions the sharp value of the constant c in the condition ‖B‖ < cd implying the solvability of the operator Riccati equation XA−CX+XBX = B∗ is equal to √ 2. We also prove an extension of the Davis-Kahan...

Existence and Uniqueness of Solutions to the Operator Riccati Equation. a Geometric Approach

We introduce a new concept of unbounded solutions to the operator Riccati equation A1X − XA0 − XV X + V ∗ = 0 and give a complete description of its solutions associated with the spectral graph subspaces of the block operator matrix B = ( A0 V V ∗ A1 ) . We also provide a new characterization of the set of all contractive solutions under the assumption that the Riccati equation has a contractiv...

The solutions to the operator equation $TXS^* -SX^*T^*=A$ in Hilbert $C^*$-modules

In this paper, we find explicit solution to the operator equation $TXS^* -SX^*T^*=A$ in the general setting of the adjointable operators between Hilbert $C^*$-modules, when $T,S$ have closed ranges and $S$ is a self adjoint operator.

Existence Condition on Solutions to the Algebraic Riccati Equation

First, the existence conditions on the solutions to the algebraic Riccati equation are reviewed. Then, a strict proof is presented for a necessary and sufficient condition on the existence of a unique optimal positive definite solution to this equation. By using this condition, some untrue results on the design of robust decentralized controllers are corrected.

A Geometric Characterization of Solutions to The Algebraic Riccati Equation