Potential Function Methods for Approximately Solving LinearProgrammingProblems INTERNATIONALSERIESIN OPERATIONS RESEARCH & MANAGEMENT SCIENCE Frederick S. Hillier, Series Editor Stanford University Miettinen, K. M. / NONLINEAR MULTIOBJECTIVE OPTIMIZATION Chao, H. & Huntington, H. G. / DESIGNING COMPETITIVE ELECTRICITY MARKETS Weglarz, J./ PROJECTSCHEDULING: RecentModels, Algorithms& Applications Sahin, I. & Polatoglu, H. / QUALITY,WARRANTYAND PREVENTIVE MAINTENANCE Tavares, L. V. / ADVANCED MODELS FOR PROJECT MANAGEMENT Tayur, S., Ganeshan, R. & Magazine, M. / QUANTITATIVE MODELING FOR SUPPLY CHAINMANAGEMENT Weyant,J./ENERGYAND ENVIRONMENTAL POLICY MODELING Shanthikumar,J.G.&Sumita,U./APPLIED PROBABILITY AND STOCHASTIC PROCESSES Liu,B.&Esogbue,A.O./DECISION CRITERIA AND OPTIMAL INVENTORY PROCESSES Gal, T., Stewart, T.J., Hanne, T./ MULTICRITERIA DECISIONMAKING: Advances inMCDM Models, Algorithms,Theory,andApplications Fox, B. 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Solving LinearProgramming Problems POTENTIAL FUNCTION METHODS FOR APPROXIMATELY SOLVING LINEAR PROGRAMMING PROBLEMS: THEORY AND PRACTICE DANIEL BIENSTOCK Department of IEOR Columbia University New York KLUWER ACADEMIC PUBLISHERS NEW YORK, BOSTON, DORDRECHT, LONDON, MOSCOW eBookISBN: 0-306-47626-6 Print ISBN: 1-4020-7173-6 ©2002 Kluwer Academic Publishers NewYork, Boston, Dordrecht, London, Moscow Print ©2002 Kluwer Academic Publishers Dordrecht All rights reserved No part of this eBook maybe reproducedor transmitted inanyform or byanymeans,electronic, mechanical, recording, or otherwise,withoutwritten consent from the Publisher Createdin the UnitedStates of America Visit Kluwer Online at: http://kluweronline.com and Kluwer's eBookstoreat: http://ebooks.kluweronline.com Contents List of Figures ix List of Tables xi Preface xiii 1 Introduction xv 1. EARLY ALGORITHMS 1 1 The Flow Deviation Method 3 1.1 Convergence Analysis 5 1.2 Analysis of the Flow Deviation method 8 1.3 Historical Perspective 11 2 The Shahrokhi and Matula Algorithm 13 2.1 The algorithm proper 19 2.2 Cut metrics and minimum congestion 22 2.2.1 Cut metrics and capacitated network design 23 2. THE EXPONENTIAL POTENTIAL FUNCTION – KEY IDEAS 27 0.2.2 Handling more general problems 27 0.2.3 Handling large width 28 0.2.4 Leveraging block-angularstructure 30 1 A basic algorithm for min-max LPs 30 1.1 The first stage 31 1.2 The second stage 32 1.3 Computing to absolute tolerance 33 2 Round-robin and randomized schemes for block-angular problems 39 2.1 Basic deterministic approach 41 2.2 Randomized approaches 43 vi APPROXIMATELY SOLVING LARGE LINEAR PROGRAMS 2.3 What is best 44 3 Optimization and more general feasibility systems 44 4 Width, revisited 47 5 Alternative potential functions 48 6 A philosophical point: why these algorithms are useful 48 3. RECENT DEVELOPMENTS 51 1 Oblivious rounding 51 1.1 Concurrent flows 54 1.1.1 The oracle 55 1.1.2 The deterministic algorithm 57 1.1.3 Handling general capacities 59 1.1.4 Comparison with the exponential potential function method 62 2 Lower bounds for Frank-Wolfe methods 62 2.1 Lower bounds under the oracle model 64 3 The algorithms of Garg-Könemann and Fleischer 66 3.1 The Luby-Nisan algorithm and related work 67 4 Lagrangian Relaxation, Non-Differentiable Optimization and Penalty Methods 69 4.0.1 Bundle and cutting-plane methods 70 4.0.2 Penalty methods 70 4.0.3 The Volume algorithm 71 4. COMPUTATIONAL EXPERIMENTS 73 0.1 Remarks on previous work 74 0.2 Outline of a generic implementation 76 1 Basic Issues 78 1.1 Choosing a block 78 1.2 Choosing 79 1.3 Choosing 80 1.4 Choosing 81 2 Improving Lagrangian Relaxations 83 3 Restricted Linear Programs 86 4 Tighteningformulations 88 5 Computational tests 89 5.1 Network Design Models 90 5.2 Minimum-cost multicommodity flow problems 91 5.3 Maximum concurrent flow problems 93 Contents vii 5.4 More sophisticated network design models 94 5.5 Empirical trade-offbetween time and accuracy 97 5.6 Hitting the sweet spot 98 6 Future work 101 APPENDIX - FREQUENTLY ASKED QUESTIONS 103 References 107 Index 111 This Page Intentionally Left Blank List of Figures 0.1 Time as a functionofcolumns fordual simplex on concurrentflowproblems;best-fit cubic xvii 0.2 Timeasafunctionofcorrect digitsforBarriercode oninstancenetd9 xviii 4.1 Time as a function of column count for poten- tial function methodonRMFGEN concurrentflow problems 95 4.2 Timeasfunctionof for instancermfgen2 99 4.3 Time as functionof for instance netd9 100