Combinatorics and Commutative Algebra

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Springer Science+Business Media, LLC

Richard P. Stanley

Combinatorics and Commutative Algebra

Springer Science+Business Media, LLC 1983

Author: Richard P. Stanley Mathematics Department, 2-375 Massachusetts Institute of Technology Cambridge, MA 02139

Library of Congress Cataloging in PubUcation Data Stanley, Richard P., 1944Combinatorics and commutative algebra. (Progress in mathematics ; v. 41) Bibliography: p. 1. Commutative algebra. 2. Combinatorial analysis. I. Title. 11. Series: Progress in mathematics ; 41. QA251.3.S72 1983 512'.24 83-17915

CIP-Kurztitelaufnahme der Deutschen Bibliothek StanIey, Ricbard P.: Combinatorics and commutative algebra/ Richard P. Stanley. - Boston; Basel; Stuttgart : Birkhäuser, 1983. (Progress in mathematics ; 41) NE:GT ISBN 978-0-8176-3112-3 ISBN 978-1-4899-6752-7 (eBook) DOI 10.1007/978-1-4899-6752-7 All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without prior permission of the copyright owner.

© Springer Science+Business Media New York 1983 Originally published by Birkhäuser Boston, Inc in1983. Softcover reprint of the hardcover 1st edition 1983 ABCDEFGHIJ

TABlE OF CONTENTS Preface Notation Chapter 0

vii viii BACKGROUND § §

§

Chapter I

10 2. 3 0

7 22

NONNEGATIVE INTEGRAL SOLUTIONS TO LINEAR EQUATIONS l. 2. 3.

4. 5. 6.

7. 8. §

9.

§1O. § ll. § 12. § 13.

Chapter II

Combinatorics Commutative algebra and homological algebra Topo 1ogy

Integer stochastic matrices (magie squares) Graded algebras and modules Elementary aspects of JIJ -sol utions to linear equations Integer stochastic matrices again Dimension, depth, and Cohen-Macaulay modules local cOhomology Local cohomology of the modules Mffi'>',0: Reci proc ity Reciprocity for integer stochastic matrices Rational points in integral polytopes Free resolutions Duality and canonical modules A final look at linear equations

30 31

33 37 39 43 45

50

51

52 54

56 60

THE FACE RING OF f\ SH1PLICIAL COMPLEX 1. 2. 3. 4. 5. 6. 7. 8.

Elementary properties of the face ring f-vectors and h-vectors of complexes and multicomplexes Cohen-Macaulay complexes and the Upper Bound Conjecture Homological properties of face rings Gorenstein face rings Gorenstein Hilbert functions Canonical modules of face rings Buchsbaum complexes

62 64 68 70 74 77 80 84

86

References

v

PREFACE

These notes are based on aseries of eight lectures given at the University of Stockholm during April and May, 1981.

They were intended

to give an overview of two topics from "combinatorial commutative algebra", viz., (1) solutions to 1 inear equations in nonnegative . integers (wh ich is equivalent to the theory of invariants of a torus acting 1 inearly on a polynomial ring), and (2) the face ring of a simpl i ci al compl ex.

In order to give a broad perspect ive many detai ls

and special ized topics have been regretfully omitted.

In general,

proofs have been provided only for those res