P1:JYS book1 CUUS259-Nagamochi 9780521878647 July16,2008 14:23 AlgorithmicAspectsofGraphConnectivity AlgorithmicAspectsofGraphConnectivityisthefirstbookthatthoroughlydiscusses graphconnectivity,acentralnotioningraphandnetworktheory,emphasizingitsal- gorithmic aspects. This book contains various definitions of connectivity, including edge-connectivity,vertex-connectivity,andtheirramifications,aswellasrelatedtop- ics such as flows and cuts. With wide applications in the fields of communication, transportation,andproduction,graphconnectivityhasmadetremendousalgorithmic progressundertheinfluenceoftheoryofcomplexityandalgorithmsinmoderncom- puter science. New concepts and graph theory algorithms that provide quicker and moreefficientcomputing,suchasMA(maximumadjacency)orderingofvertices,are comprehensivelydiscussed. Covering both basic definitions and advanced topics, this book can be used as a textbookingraduatecoursesofmathematicalsciences(suchasdiscretemathematics, combinatorics, and operations research) in addition to being an important reference bookforallspecialistsworkingindiscretemathematicsanditsapplications. HiroshiNagamochiisaprofessorattheGraduateSchoolofInformatics,KyotoUniver- sity.HeisamemberoftheOperationsResearchSocietyofJapanandtheInformation ProcessingSociety. ToshihideIbarakiisaprofessorwithKwanseiGakuinUniversityandprofessoremer- itusofKyotoUniversity.HeisaFellowoftheACM;OperationsResearchSocietyof Japan;theInstituteofElectronic,InformationandCommunicationEngineers;andthe InformationProcessingSociety. i P1:JYS book1 CUUS259-Nagamochi 9780521878647 July16,2008 14:23 ii P1:JYS book1 CUUS259-Nagamochi 9780521878647 July16,2008 14:23 ENCYCLOPEDIA OF MATHEMATICS AND ITS APPLICATIONS FOUNDING EDITOR G.-C. ROTA EditorialBoard R.Doran,P.Flajolet,M.Ismail,T.-Y.Lam,E.Lutwak Thetitlesbelow,andearliervolumesintheseries,areavailablefrombooksellersorfrom CambridgeUniversityPressatwww.cambridge.org. 90 M.Lothaire AlgebraicCombinatoricsonWords 91 A.A.IvanovandS.V.Shpectorov GeometryofSporadicGroupsII 92 P.McMullenandE.Schulte AbstractRegularPolytopes 93 G.Gierzetal. ContinuousLatticesandDomains 94 S.Finch MathematicalConstants 95 Y.Jabri TheMountainPassTheorem 96 G.GasperandM.Rahman BasicHypergeometricSeries,2ndedn 97 M.C.PedicchioandW.Tholen(eds.) CategoricalFoundations 98 M.E.H.Ismail ClassicalandQuantumOrthogonalPolynomialsinOneVariable 99 T.Mora SolvingPolynomialEquationSystemsII 100 E.OlivieriandM.Eula´liaVares LargeDeviationsandMetastability 101 A.Kushner,V.Lychagin,andV.Rubtsov ContactGeometryandNonlinear DifferentialEquations 102 L. W.Beineke,R.J.Wilson,andP.J.Cameron(eds.) TopicsinAlgebraicGraph Theory 103 O.Staffans Well-PosedLinearSystems 104 J.M.Lewis,S.Lakshmivarahan,andS.Dhall DynamicDataAssimilation 105 M.Lothaire AppliedCombinatoricsonWords 106 A.Markoe AnalyticTomography 107 P.A.Martin MultipleScattering 108 R.A.Brualdi CombinatorialMatrixClasses 110 M.-J.LaiandL.L.Schumaker SplineFunctionsonTriangulations 111 R.T.Curtis SymmetricGenerationofGroups 112 H.Salzmann,T.Grundho¨fer,H.Ha¨hl,andR.Lo¨wen TheClassicalFields 113 S.PeszatandJ.Zabczyk StochasticPartialDifferentialEquationswithLe´vy Noise 114 J.Beck CombinatorialGames 116 D.Z.ArovandH.Dym J-ContractiveMatrixValuedFunctionsandRelated Topics 117 R.Glowinski,J.-L.LionsandJ.He ExactandApproximateControllabilityfor DistributedParameterSystems 118 A.A.BorovkovandK.A.Borovkov AsymptoticAnalysisofRandomWalks 119 M.DezaandM.DutourSikiric´ GeometryofChemicalGraphs 120 T.Nishiura AbsoluteMeasurableSpaces 121 F.King HilbertTransforms 122 S.Khrushchev OrthogonalPolynomialsandContinuedFractions:FromEuler’s PointofView iii P1:JYS book1 CUUS259-Nagamochi 9780521878647 July16,2008 14:23 iv P1:JYS book1 CUUS259-Nagamochi 9780521878647 July16,2008 14:23 encyclopedia of mathematics and its applications Algorithmic Aspects of Graph Connectivity HIROSHI NAGAMOCHI KyotoUniversity TOSHIHIDE IBARAKI KwanseiGakuinUniversity v P1:JYS book1 CUUS259-Nagamochi 9780521878647 July16,2008 14:23 CAMBRIDGEUNIVERSITYPRESS Cambridge,NewYork,Melbourne,Madrid,CapeTown,Singapore,Sa˜oPaulo,Delhi CambridgeUniversityPress 32AvenueoftheAmericas,NewYork,NY10013-2473,USA www.cambridge.org Informationonthistitle:www.cambridge.org/9780521878647 (cid:1)C HiroshiNagamochiandToshihideIbaraki2008 Thispublicationisincopyright.Subjecttostatutoryexception andtotheprovisionsofrelevantcollectivelicensingagreements, noreproductionofanypartmaytakeplacewithout thewrittenpermissionofCambridgeUniversityPress. Firstpublished2008 PrintedintheUnitedStatesofAmerica AcatalogrecordforthispublicationisavailablefromtheBritishLibrary. LibraryofCongressCataloginginPublicationData Nagamochi,Hiroshi,1960– Algorithmicaspectsofgraphconnectivity/HiroshiNagamochiandToshihideIbaraki. p. cm. Includesindex. ISBN978-0-521-87864-7(hardback) 1.Graphconnectivity. 2.Graphalgorithms. I.Ibaraki,Toshihide. II.Title. QA166.243.N34 2008 511(cid:2).5–dc22 2008007560 ISBN 978-0-521-87864-7hardback CambridgeUniversityPresshasnoresponsibilityfor thepersistenceoraccuracyofURLsforexternalor third-partyInternetWebsitesreferredtointhispublication anddoesnotguaranteethatanycontentonsuch Websitesis,orwillremain,accurateorappropriate. vi P1:JYS book1 CUUS259-Nagamochi 9780521878647 July16,2008 14:23 Contents Preface pageix Notation xi 1 Introduction 1 1.1 PreliminariesofGraphTheory 1 1.2 AlgorithmsandComplexities 13 1.3 FlowsandCuts 20 1.4 ComputingConnectivities 34 1.5 RepresentationsofCutStructures 45 1.6 ConnectivitybyTrees 57 1.7 TreeHypergraphs 60 2 MaximumAdjacencyOrderingandForestDecompositions 65 2.1 SpanningSubgraphsPreservingConnectivity 65 2.2 MAOrdering 73 2.3 3-Edge-ConnectedComponents 86 2.4 2-ApproximationAlgorithmsforConnectivity 100 2.5 FastMaximum-FlowAlgorithms 107 2.6 TestingChordality 112 3 MinimumCuts 114 3.1 PendentPairsinMAOrderings 114 3.2 AMinimum-CutAlgorithm 117 3.3 s-Properk-Edge-ConnectedSpanningSubgraphs 119 3.4 AHierarchicalStructureofMAOrderings 123 3.5 MaximumFlowsBetweenaPendentPair 127 3.6 AGeneralizationofPendentPairs 130 3.7 PracticallyEfficientMinimum-CutAlgorithms 131 4 CutEnumeration 137 4.1 EnumeratingAllCuts 137 4.2 EnumeratingSmallCuts 140 vii P1:JYS book1 CUUS259-Nagamochi 9780521878647 July16,2008 14:23 viii Contents 4.3 EnumeratingMinimumCuts 145 4.4 UpperBoundsontheNumberofSmallCuts 149 5 CactusRepresentations 153 5.1 CanonicalFormsofCactusRepresentations 153 5.2 (s,t)-CactusRepresentations 171 5.3 ConstructingCactusRepresentations 180 6 ExtremeVertexSets 191 6.1 ComputingExtremeVertexSetsinGraphs 192 6.2 AlgorithmforDynamicEdgesIncidenttoaSpecifiedVertex 198 6.3 OptimalContractionOrdering 200 6.4 Minimumk-SubpartitionProblem 207 7 EdgeSplitting 217 7.1 Preliminaries 217 7.2 EdgeSplittinginWeightedGraphs 220 7.3 EdgeSplittinginMultigraphs 226 7.4 OtherSplittings 232 7.5 Detachments 237 7.6 ApplicationsofSplittings 240 8 ConnectivityAugmentation 246 8.1 IncreasingEdge-ConnectivitybyOne 247 8.2 StarAugmentation 249 8.3 AugmentingMultigraphs 252 8.4 AugmentingWeightedGraphs 254 8.5 MoreonAugmentation 276 9 SourceLocationProblems 282 9.1 SourceLocationProblemUnderEdge-Connectivity Requirements 283 9.2 SourceLocationProblemUnderVertex-Connectivity Requirements 295 10 SubmodularandPosimodularSetFunctions 304 10.1 SetFunctions 304 10.2 MinimizingSubmodularandPosimodularFunctions 306 10.3 ExtremeSubsetsinSubmodularandPosimodularSystems 315 10.4 OptimizationProblemsoverSubmodularandPosimodular Systems 320 10.5 ExtremePointsofBasePolyhedron 336 10.6 MinimumTransversalinSetSystems 342 Bibliography 357 Index 371 P1:JYS book1 CUUS259-Nagamochi 9780521878647 July16,2008 14:23 Preface Because the concept of a graph was introduced to represent how objects are connected,itisnotsurprisingthatconnectivityhasbeenacentralnotioningraph theory since its birth in the 18th century. Various definitions of connectivities havebeenproposed,forexample,edge-connectivity,vertex-connectivity,andtheir ramifications.Closelyrelatedtoconnectivityareflowsandcutsingraphs,where thecutmayberegardedasadualconceptofconnectivityandflows. A recent general trend in the research of graph theory appears as a shift to its algorithmic aspects, and improving time and space complexities has been a strongincentivefordevisingnewalgorithms.Thisisalsotruefortopicsrelatedto connectivities,flows,andcuts,andmuchimportantprogresshasbeenmade.Such topicsincludecomputation,enumeration,andrepresentationofallminimumcuts and small cuts; new algorithms to augment connectivity of a given graph; their generalization to more abstract mathematical systems; and so forth. In view of these,itwouldbeatimelyattempttosummarizethoseresultsandpresentthemin aunifiedsettingsothattheycanbesystematicallyunderstoodandcanbeapplied tootherrelatedfields. In these developments, we observe that a simple tool known as maximum adjacency (MA) ordering has been a profound influence on the computational complexityofalgorithmsforanumberofproblems.Itisdefinedasfollows. MA ordering: Given a graph G =(V,E), a total ordering σ =(v , 1 v2,...,vn) of vertices is an MA ordering if |E(Vi−1,vi)|≥|E(Vi−1,vj)| holds for all i, j with 2≤i < j ≤n, where V ={v ,v ,...,v } and i 1 2 i E(V(cid:2),v)isthesetofedgesfromverticesinV(cid:2) tov. To our knowledge, MA ordering was first introduced in a paper by R. E. Tarjan and M.Yannakakis [300],where itwas called theMaximum Cardinality Search and used to test chordality of graphs, to test acyclicity of hypergraphs, and to solveotherproblems.WethenrediscoveredMAordering[232],showingthatitis effectiveforproblemssuchasfindingaforestdecompositionandcomputingthe ix
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