DISCRETE  CONVEX  ANALYSIS
SIAM Monographs  on
Discrete Mathematics and Applications
The series includes advanced monographs  reporting  on the most  recent  theoretical,  computational, or
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Editor-in-Chief
Peter  L. Hammer,  RUTCOR,  Rutgers,  The State  University  of New Jersey
Editorial  Board
M. Aigner,  Freie  Universitat Berlin,  Germany
N. Alon,  Tel Aviv University, Israel
E. Balas, Carnegie Mellon  University, USA
J-  C. Bermond,  UniversitedeNice-SophiaAntipolis,  France
J. Berstel,  Universite Marne-la-Vallee,  France
N. L. Biggs, The London School of Economics,  United  Kingdom
B. Bollobas, University of Memphis,  USA
R. E. Burkard,  Technische Universitat  Graz, Austria
D. G. Cornell,  University of Toronto, Canada
I. Gessel,  Brandeis  University, USA
F. Glover,  University of Colorado,  USA
M. C. Golumbic, Bar-Han University, Israel
R. L. Graham,  AT&T Research,  USA
A. J. Hoffman,  IBM  T. J.  Watson Research Center, USA
T. Ibaraki, Kyoto University, Japan
H. Imai,  University of  Tokyo,  Japan
M. Karoriski,  Adam  Mickiewicz  University, Poland, and Emory
University,  USA
R. M. Karp,  University of Washington, USA
V. Klee,  University of Washington,  USA
K. M. Koh,  National  University of Singapore,  Republic of
Singapore
B. Korte,  Universitat Bonn,  Germany
A. V. Kostochka,  Siberian Branch of the Russian Academy  of
Sciences, Russia
F. T. Leighton, Massachusetts  Institute of  Technology, USA
T. Lengauer,  Gesellschaft fur Mathematik  und
Datenverarbeitung  mbH,  Germany
S. Martello,  DEIS University of Bologna,  Italy
M. Minoux,  Universite Pierre et Marie Curie, France
R. Mb'hring,  Technische Universitat Berlin,  Germany
C. L. Monma, Bellcore, USA
J. Nesetril,  Charles  University, Czech  Republic
W. R. Pulleyblank, IBM  T. J.  Watson Research  Center, USA
A. Recski,  Technical University of Budapest,  Hungary
C. C. Ribeiro,  Catholic University of Rio de Janeiro,  Brazil
H. Sachs,  Technische Universitat llmenau,  Germany
A. Schrijver,  CWI, The  Netherlands
R. Shamir,  Tel Aviv  University, Israel
N. J. A. Sloane,  AT&T Research, USA
W. T. Trotter,  Arizona  State University, USA
D. J. A. Welsh,  University of Oxford,  United Kingdom
D. de Werra,  Ecole Polytechnique  Federate de Lausanne,
Switzerland
P. M. Winkler,  Bell Labs, Lucent  Technologies, USA
Yue Minyi,  Academia  Sinica, People's  Republic of China
Series  Volumes
Murota,  K., Discrete Convex Analysis
Toth,  P. and Vigo,  D.,  The  Vehicle Routing  Problem
Anthony,  M., Discrete Mathematics  of Neural Networks:  Selected  Topics
Creignou,  N., Khanna, S., and Sudan, M., Complexity  Classifications of Boolean  Constraint Satisfaction  Problems
Hubert, L., Arable,  P., and Meulman, J., Combinatorial  Data Analysis:  Optimization by Dynamic  Programming
Peleg,  D., Distributed  Computing: A Locality-Sensitive  Approach
Wegener,  I., Branching  Programs and Binary Decision Diagrams:  Theory  and  Applications
Brandstadt, A., Le, V. B., and Spinrad, J. P., Graph Classes: A Survey
McKee,  T. A. and  McMorris,  F. R.,  Topics in Intersection  Graph  Theory
Grilli di Cortona, P., Manzi,  C., Pennisi, A., Ricca,  R, and Simeone,  B., Evaluation and Optimization of Electoral  Systems
DISCRETE  CONVEX  ANALYSIS
KAZUO  MUROTA
University of Tokyo; PRESTO, JST
Tokyo, Japan
Society for Industrial  and Applied Mathematics
Philadelphia
Copyright  © 2003 by  the  Society  for Industrial and  Applied Mathematics.
10 9 8 7 6 5 4 3 21
All rights reserved.  Printed  in the  United  States of America.  No part  of this book  may
be  reproduced, stored,  or transmitted in any manner without the written  permission of
the  publisher.  For  information,  write  to  the  Society  for  Industrial  and  Applied
Mathematics,  3600 University City Science  Center,  Philadelphia, PA  19104-2688.
library of Congress Cataloging-in-Publication Data
Murota,  Kazuo,  1955-
Discrete  convex  analysis /  Kazuo Murota.
p.  cm. —  (SIAM  monographs  on  discrete  mathematics and  applications)
Includes  bibliographical  references  and  index.
ISBN  0-89871-540-7
1. Convex  functions. 2. Convex  sets.  3. Mathematical analysis.  I. Title. II. Series.
QA331.5.M87 2003
515'.8—dc21
2003042468
is a registered  trademark.
Contents
List  of Figures 
Notation 
Preface 
1 
Introduction to the  Central  Concepts 
1.1 
1.2 
1.3 
1.4 
Aim 
History 
Aim and  History  of Discrete  Convex Analysis 
1.1.1 
1.1.2 
Useful  Properties  of Convex  Functions 
Submodular  Functions  and  Base  Polyhedra 
Submodular  Functions 
1.3.1 
1.3.2 
Base  Polyhedra 
Discrete Convex  Functions 
1.4.1 
1.4.2 
1.4.3 
1.4.4 
1.4.5 
L-Convex Functions 
M-Convex Functions 
Conjugacy 
Duality 
Classes of Discrete Convex Functions 
Bibliographical Notes 
2  Convex Functions with  Combinatorial  Structures 
2.1 
2.2 
2.3 
Convex Quadratic  Functions 
Symmetric M-Matrices 
Combinatorial  Property  of Conjugate Functions 
General  Quadratic  L-/M-Convex Functions 
Quadratic  Functions 
2.1.1 
2.1.2 
2.1.3 
2.1.4 
Nonlinear Networks 
2.2.1 
2.2.2 
2.2.3 
Substitutes  and  Complements  in Network Flows 
2.3.1 
Real-Valued Flows 
Integer-Valued  Flows 
Technical  Supplements 
Convexity and  Submodularity 
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xxi
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1
1
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9
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Contents
2.3.2 
2.4  Matroids 
2.4.1 
2.4.2 
Bibliographical  Notes 
Technical  Supplements 
63
68
Prom  Matrices to  Matroids 
68
From  Polynomial Matrices to  Valuated  Matroids  .  .  71
74
3  Convex  Analysis, Linear  Programming,  and Integrality 
Convex Analysis 
Linear Programming 
Integrality  for  a Pair  of Integral  Polyhedra 
Integrally  Convex Functions 
3.1 
3.2 
3.3 
3.4 
Bibliographical Notes 
4  M-Convex  Sets  and Submodular  Set  Functions 
Definition 
Exchange  Axioms 
Submodular  Functions  and  Base  Polyhedra 
Polyhedral  Description of M-Convex Sets 
Submodular  Functions  as Discrete  Convex Functions 
4.1 
4.2 
4.3 
4.4 
4.5 
4.6  M-Convex Sets as  Discrete  Convex Sets 
4.7 
4.8  M-Convex Polyhedra 
Bibliographical Notes 
M^-Convex  Sets 
5 
L-Convex Sets and Distance  Functions 
5.1 
5.2 
5.3 
5.4 
5.5 
5.6 
Bibliographical  Notes 
Definition 
Distance  Functions  and  Associated  Polyhedra 
Polyhedral  Description of L-Convex Sets 
L-Convex Sets  as  Discrete Convex Sets 
L^-Convex  Sets 
L-Convex Polyhedra 
6  M-Convex  Functions 
Local Exchange  Axiom 
Examples 
Basic  Operations 
Supermodularity 
Descent  Directions 
6.1  M-Convex Functions  and  M^-Conyex Functions 
6.2 
6.3 
6.4 
6.5 
6.6 
6.7  Minimizers 
6.8 
6.9 
6.10  Convex Extension 
6.11 
6.12 
Polyhedral  M-Convex Functions 
Positively  Homogeneous  M-Convex Functions 
Gross Substitutes  Property 
Proximity  Theorem 
77
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Ill
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164
Contents 
6.13  Directional Derivatives and  Subgradients 
6.14  Quasi  M-Convex Functions 
Bibliographical Notes 
7 
L-Convex Functions  and  L''-Convex Functions 
Discrete  Midpoint Convexity 
Examples 
Basic  Operations 
L-Convex Functions 
7.1 
7.2 
7.3 
7.4 
7.5  Minimizers 
7.6 
7.7 
7.8 
7.9 
7.10  Directional Derivatives and  Subgradients 
7.11  Quasi  L-Convex Functions 
Bibliographical Notes 
Proximity Theorem 
Convex Extension 
Polyhedral  L-Convex Functions 
Positively  Homogeneous L-Convex Functions 
8  Conjugacy  and Duality 
8.1 
8.2 
Conjugacy 
8.1.1 
8.1.2 
8.1.3 
Duality 
8.2.1 
8.2.2 
8.2.3 
Submodularity under  Conjugacy 
Polyhedral M-/L-Convex Functions 
Integral  M-/L-Convex Functions 
Separation  Theorems 
Fenchel-Type  Duality Theorem 
Implications 
8.3  M2-Convex Functions and  L2-Convex Functions 
8.4 
M2-Convex Functions 
L2-Convex Functions 
Relationship 
8.3.1 
8.3.2 
8.3.3 
Lagrange Duality  for Optimization 
8.4.1 
8.4.2 
8.4.3 
8.4.4 
Outline 
General Duality Framework 
Lagrangian  Function Based  on M-Convexity 
Symmetry in Duality 
Bibliographical Notes 
9  Network Flows 
9.1  Minimum Cost  Flow and  Fenchel Duality 
Minimum Cost  Flow Problem 
Feasibility 
Optimality  Criteria 
Relationship  to  Fenchel Duality 
9.1.1 
9.1.2 
9.1.3 
9.1.4 
9.2  M-Convex Submodular Flow Problem 
9.3 
Feasibility  of Submodular Flow Problem 
vii
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. . ..  238
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