Ergodic Theory, Entropy

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214 Meir Smorodinsky University of Warwick, Coventry Warwickshire/G.B.

Ergodic Theory, Entropy

Springer-Verlag Berlin· Heidelberg· NewYork 1971

AMS Subject Classifications (1970): 28A65, 47A35, 94A15

ISBN 3-540-05556-8 Springer-Verlag Berlin' Heidelberg· New York ISBN 0-387-05556-8 Springer-Verlag New York . Heidelberg· Berlin

This work is subject to copyright. All rights are reserved, whether the whole or part of the material is concerned, specifically those of translation, reprinting, re-use of illustrations, broadcasting, reproduction by photocopying machine or similar means, and storage in data banks. Under § 54 of rhe German Copyright Law where copies are made for other than private use, a fee is payable to the publisher, the amount of the fee to be determined by agreement with the publisher.

© by Springer-Verlag Berlin' Heidelberg 1971. Library of Congress Catalog Card Number 75-171482. Printed in Germany. Offsetdruck: ] ulius Beltz, HemsbachiBergstr.

PHEFACE

These notes are based on one term's M.Sc. course given in Warwick University, Autumn 1970.

for the course was

basic knowledge of measure theory and integration such as covered by

[1].

Espacially, the Radon Nikodym theorem is assumed.

In the history of Ergodic Theory there were three major breakthroughs.

The first was Birkhoff's individual ergodic theorem(lJ

The second was the introduction of entropy by Kollllogorov (1)[2) and Sinai (1].

The third was Sinai's weak isomorphism [2] and Ornstein's

isomorphisms theorem for

[4][5].

shifts and other results [1](2](3)

See also Friedman, Ornstein [1].

All these steps were Since my purpose was to

achieved without the use of spectral theory. introduce the stUdents

to the recent development, I chose to

omit spectral theory from the discussion.

Other important and

beautiful topics which are not mentioned are ergodic theory of operators, the problem of invariant measures and measurable transformation on spaces of infinite measure. expository works: Friedman [1] ;

We refer the reader to the following

Billingsley [1] ; Halmos [2]

Hokhlin [2] : and Sinai

Jacobs [1] ;

[4].

In the treatment of entropy theory I avoided using uncountable partitions and preferred the use of sub-a-fields.

80, these notes

are in the spirit of Billingsley [1) rather than Parry [i ], Rokhlin and Sinai [4). The symbol

invites the reader to complete a missing

arguement, or sometimes, a whole proof.

C2J

IV

I am grateful to the Mathematical Reseach Institute of Warwick University in which I was a Senior Research Fellow while writing these notes. My thanks go to Mr R. Keppler who assisted me in organizing parts of the notes and to Mrs Sue Elworthy for her patient job of them.

Mathematics Institute, Warwick University.

M.S.

fuarch

TABLE OF CONTENTS

Notation, Symbols Chapter I Chapter II Chapter III Chapter IV Chapter V

Examples

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..

2

.. ··..···· 8 Conditional Probabilities and Expectations. Doob's Martingale Theorem 13 ...· Entropy and Conditional Entropy 19 ··.. Entropy of a Transformation . · · ·