Commuting Nonselfadjoint Operators in Hilbert Space Two Independent

Classification of commuting non-selfadjoint operators is one of the most challenging problems in operator theory even in the finite-dimensional case. The spectral analysis of dissipative operators has led to a series of deep results in the framework of un

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1272

Moshe S. Livsic Leonid L. Waksman

Commuting Nonselfadjoint Operators in Hilbert Space Two Independent Studies

Spri nger-Verlag Berlin Heidelberg New York London Paris Tokyo

Authors

Moshe S. Livsic Dept. of Mathematics Beer Sheva Ben-Gurion University of the Negev, Israel Leonid L. Waksman ul. 1 konnoi Armii d. 18/9 kv. 6 344029 Rostov-na-Donu, USSR

Mathematics Subject Classification (1980): 15, 35A07, 46, 47, 47005, 47H06, 73,81,93 ISBN 3-540-18316-7 Springer-Verlag Berlin Heidelberg New York ISBN 0-387-18316-7 Springer-Verlag New York Berlin Heidelberg

This work is subject to copyright. All rights are reserved, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, re-use of illustrations, recitation, broadcasting, reproduction on microfilms or in other ways, and storage in data banks. Duplication of this publication or parts thereof is only permitted under the provisions of the German Copyright Law of September 9, 1965, in its version of June 24, 1985, and a copyright fee must always be paid. Violations fall under the prosecution act of the German Copyright Law.

© Springer-Verlag Berlin Heidelberg 1987 Printed in Germany Printing and binding: Druckhaus Beltz, Hemsbach/Bergstr. 2146/3140-543210

Commuting Nonselfadjoint Operators in Hilbert Space

. v.

M.S. LJ.vsJ.c: Commuting Nonselfadjoint Operators and Collective Motions of Systems •.•••.••••••.•• 1 L. Waksman: Harmonic Analysis of Mult1-Parameter Semigroups of Contractions •••••••••••••••... 40

COMMUTING NONSELFADJOINT OPERATORS AND COLLECTIVE MOTIONS OF SYSTEMS

Moshe S.

TABLE OF CONTENTS Introduction §l.

Single-Operator Colligations: Review of Basic Results

5

§2.

Commutative Colligations and Collective Motions

9

§3.

Characteristic (Transfer) Functions

14

§4.

The Output Realization of Colligations

17

§5.

Composit Colligations

22

§6.

Couplings and Resolutions of Commutative Colligations

23

§7.

A One Dimensional Wave Equation

27

§ 8.

Symmetries

32

COMMUTING NONSELFADJOINT OPERATORS AND COLLECTIVE MOTIONS OF SYSTEMS M.S. Department of Mathematics Ben Gurion University of the Negev Beer Sheva, Israel Introduction The spectral analysis of nonselfadjoint operators in the single operator case was developed during the fifties and sixties thanks to the efforts of many mathematicians. Then it was realized that this analysis forms a mathematical basis for the theory of open systems, interacting with the environment. In the light of the success of this theory, attempts have been made to create an analogous theory for several commuting operators, based on a generalization of the Nagy-Foias functional model to the case of several variables. It turned out, however, that this approach was ineffective. Moreover, the following generalization of the classical Cayley-Hamilton Theorem was obtained: Two

with by a The degree of this equation does not exceed the dimension of the sum of ranges of imaginary parts.

This result shows that the genuine theory of commuting nonselfadjoint ope