Browsing by Subject "isometry"

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Access status: Open Access ,
Characterizations of rectangular (para)-unitary rational functions
(2016) Alpay, Daniel; Jørgensen, Palle E.T.; Lewkowicz, Izchak
We here present three characterizations of not necessarily causal, rational functions which are (co)-isometric on the unit circle: (i) through the realization matrix of Schur stable systems, (ii) the Blaschke-Potapov product, which is then employed to introduce an easy-to-use description of all these functions with dimensions and McMillan degree as parameters, (iii) through the (not necessarily reducible) Matrix Fraction Description (MFD). In cases (ii) and (iii) the poles of the rational functions involved may be anywhere in the complex plane, but the unit circle (including both zero and infinity). A special attention is devoted to exploring the gap between the square and rectangular cases.
Access status: Open Access ,
Ergodic conditions and spectral properties for A-contractions
(2008) Suciu, Laurian; Suciu, Nicolae
In this paper the canonical representation of an $A$-contraction $T$ on a Hilbert space $\mathcal{H}$ is used to obtain some conditions concerning the concept of $A$-ergodicity studied in [L. Suciu, <i>Orthogonal decompositions induced by generalized contractions</i>, Acta Sci. Math. (Szeged) 70 (2004), 751–765; L. Suciu, On the ergodic $A$-contractions, Analele Universitaţii de Vest din Timişoara, Ser. Mat.-Inf. 2 (2004), 115–136; L. Suciu, Ergodic properties for regular $A$-contractions, Integral Equations and Operator Theory 56 (2006) 2, 285–299; L. Suciu, <i>Ergodic properties and saturation for A-contractions, Operator Theory: Advances and Applications</i>; Proceeding of 20th Conference on Operator Theory, Timişoara 2004, Theta 2006, 225–242]. The regular case and the case of $\mathcal{R}(A)$ closed are considered, and specifically, the $TT^{*}$-contractions are studied. Some spectral properties are also given for certain particular class of $A$-isometries.
Access status: Restricted ,
Izometrie i koizometrie
(Data obrony: 2011-09-12) Głąb, Marcin
Wydział Matematyki Stosowanej
Access status: Restricted ,
Rozkłady par przemiennych izometrii działających w przestrzeniach Hilberta
(Data obrony: 2015-11-18) Kojder, Magdalena
Wydział Matematyki Stosowanej
Access status: Restricted ,
Uogólnienie twierdzenia dylatacyjnego Andô i przykładu Parrotta
(Data obrony: 2014-07-04) Koutny, Kamila
Wydział Matematyki Stosowanej
Access status: Restricted ,
Wybrane elementy teorii dylatacji
(Data obrony: 2014-07-10) Wolińska, Natalia
Wydział Matematyki Stosowanej