Discrete Spectral Synthesis and Its Applications

In order to study discrete Abelian groups with wide range applications, the use of classical functional equations, difference and differential equations, polynomial ideals, digital filtering and polynomial hypergroups is required. This book covers several

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László Székelyhidi

Discrete Spectral Synthesis and Its Applications

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László Székelyhidi University of Debrecen Institute of Mathematics H-4010 Debrecen, Hungary email: [email protected]

A C.I.P. Catalogue record for this book is available from the Library of Congress.

ISBN-10 ISBN-13 ISBN-10 ISBN-13

1-4020-4636-7 (HB) 978-1-4020-4636-0 (HB) 1-4020-4637-5 (e-Book) 978-1-4020-4637-7 (e-Book)

Published by Springer, P.O. Box 17, 3300 AA Dordrecht, The Netherlands. www.springer.com

Printed on acid-free paper

All Rights Reserved c 2006 Springer  No part of this work may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, microfilming, recording or otherwise, without written permission from the Publisher, with the exception of any material supplied specifically for the purpose of being entered and executed on a computer system, for exclusive use by the purchaser of the work.

To my sons and my wife

Contents

Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ix 1

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1

2

Spectral synthesis and spectral analysis . . . . . . . . . . . . . . . . . . . . 7 2.1 The basic problems of spectral analysis and spectral synthesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 2.2 Spectral analysis and synthesis on L1 (G) . . . . . . . . . . . . . . . . . . . 8 2.3 Spectral analysis and synthesis on L∞ (G) . . . . . . . . . . . . . . . . . . 11 2.4 Spectral analysis and synthesis on C(G) . . . . . . . . . . . . . . . . . . . . 17

3

Spectral analysis and spectral synthesis on discrete Abelian groups . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1 Spectral analysis on discrete Abelian torsion groups . . . . . . . . . . 3.2 Spectral analysis on Abelian groups . . . . . . . . . . . . . . . . . . . . . . . . 3.3 Spectral analysis on commutative semigroups . . . . . . . . . . . . . . . 3.4 Spectral synthesis and polynomial ideals . . . . . . . . . . . . . . . . . . . . 3.5 The failure of spectral synthesis on some types of discrete Abelian groups . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.6 Spectral synthesis on Abelian torsion groups . . . . . . . . . . . . . . . . 3.7 Polynomial functions and spectral synthesis . . . . . . . . . . . . . . . . .

25 25 27 27 29 34 38 42

4

Spectral synthesis and functional equations . . . . . . . . . . . . . . . . 4.1 Convolution type functional equations . . . . . . . . . . . . . . . . . . . . . . 4.2 Mean value type functional equations . . . . . . . . . . . . . . . . . . . . . . 4.3 A functional equation in digital filtering . . . . . . . . . . . . . . . . . . . .

49 49 52 60

5

Mean periodic functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.1 The Fourier transform of mean peri