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Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. The Sz.-Nagy dilation theorem (proved by Béla Sz kefalvi-Nagy) states that every contraction T on a Hilbert space H has a unitary dilation U to a Hilbert space K. Moreover, such a dilation is unique (up to unitary equivalence) when one assumes K is minimal, in the sense that the linear span of nUnK is dense in K. When this minimality condition holds, U is called the minimal unitary dilation of T. The Schaffer form of a unitary Sz. Nagy dilation can be viewed as a…mehr

Produktbeschreibung
Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. The Sz.-Nagy dilation theorem (proved by Béla Sz kefalvi-Nagy) states that every contraction T on a Hilbert space H has a unitary dilation U to a Hilbert space K. Moreover, such a dilation is unique (up to unitary equivalence) when one assumes K is minimal, in the sense that the linear span of nUnK is dense in K. When this minimality condition holds, U is called the minimal unitary dilation of T. The Schaffer form of a unitary Sz. Nagy dilation can be viewed as a beginning point for the characterization of all unitary dilations, with the required property, for a given contraction. To see that this generalises Sz.-Nagy''s theorem, note that contraction operators have the unit disc D as a spectral set, and that normal operators with spectrum in the unit circle D are unitary.