arXiv subjects
Publications and source records attributed to Dmitriy S. Kalyuzhniy.
The explicit constructions of minimal isometric, and minimal unitary dilations of an arbitrary linear pencil of operators $T(λ)=T_0+λT_1$ consisting of contractions on a separable Hilbert space for $|λ|=1$, which generalize the classical constructions (the case $T_1=0$), are presented. In contrast to the classical case these dilations are essentially non-unique.
We introduce the notion of cascade connection of multiparametric discrete time-invariant linear dynamical systems with unit delay. This allows us to construct the explicit example of conservative realization of a decomposable operator-valued function $θ(z_1, z_2)=θ_2(z_2)θ_1(z_1)$, where $θ_1$ and $θ_2$ are inner operator-valued functions on the unit disk, vanishing at zero, and discuss some properties of such realization.
We show that the factorization problem $θ(z)=θ_2(z)θ_1(z)$ is solvable in the class of Hilbert space operator-valued functions holomorphic on some neighbourhood of $z=0$ in $\nspace{C}{N}$ and having a zero at $z=0$ (here $θ(z)$ has a multiple zero at $z=0$). Such a factorization problem becomes more complicated if we demand for $θ(z), θ_1(z)$ and $θ_2(z)$ to be Agler--Schur-class functions on the polydisk $\nspace{D}{N}$ and for the factorization identity to hold in $\nspace{D}{N}$. In this case we reduce it to the problem on the existence of a cascade decomposition for certain multiparametric linear system $α$--a conservative realization of $θ(z)$, and give the criterion for its solvability in terms of common invariant subspaces for the $N$-tuple of main operators of $α$.
In the present paper we introduce the notion of dilation of a multiparametric linear stationary dynamical system (systems of this type, in particular passive, and conservative scattering ones were first introduced in func-an/9804130). We establish the criterion for existence of a conservative dilation of a multiparametric passive scattering system. This allows to distinguish the class of so-called $N$-passive systems preserving the most important properties of one-parametric passive scattering systems.
We propose the new generalization of linear stationary dynamical systems with discrete time $t\in\mathbb{Z}$ to the case $t\in\nspace{Z}{N}$. The dynamics of such a system can be reproduced by means of its associated multiparametric Lax-Phillips semigroup. We define multiparametric passive, and conservative scattering systems and interpret them in terms of operator colligations, of the associated semigroup and of "energetic" relations for system data. We prove the Agler's type theorem describing the class of holomorphic operator-valued functions on the polydisc $\nspace{D}{N}$ that are the transfer functions of multiparametric conservative scattering systems. Keywords: Passive systems, multiparametric Lax-Phillips semigroup, generalized Schur class, conservative realizations
The theorem on the existence of three commuting contractions on a Hilbert space and of a linear homogeneous matrix function of three independent variables for which the generalized von Neumann inequality fails is proved.