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1、數(shù)學(xué)雜志Vo1.34(2014)No.4MINIMUMDISTANCESPECTRALRADIUSoFGRAPHSWITHGIVENEDGECoNNECTIVITYLIXiao—xin1,2FANYi—zheng2WANGYi(.DepartmentMathematicsandComputerSciences,ChizhouUniversity,Chizhou247000,China)(2.SchoolofMathemntiealScie幾ces,AnhuiUniversity,Hefei230601,China)Abstract
2、:Inthispaperwestudytheextremalgraphswithminimumdistancespectralradiusamongallconnectedgraphsofordernandedgeconnectivityr.Byusingthecombinatorialmethod,wedeterminethatK(n一1,r)istheuniqueextremalgraph,whereg(n一1,r)isobtainedfromthecompletegraphKn一1byaddingavertexvtogeth
3、erwithedgesjoiningvtorverticesofKn一1.Alltheabovegeneralizetherelatedresultsoftheextremalgraphtheory.Keywords:graph;distancematrix;spectralradius;edgeconnectivity2010MRSubjectClassification:05C50Documentcode:AArticleID:0255—7797f2014)04-0671—081IntroductionLetGbeaconne
4、ctedsimplegraphwithvertexsetv(c)andedgesetE(G).Thedistancebetweentwoverticesu,vofG,denotedbydis,isdefinedasthelengthoftheshortestpathbetweenandvinG.ThedistancematrixofG,denotedbyD(G),isdefinedbyD(G)=(dis)u,vE(G).SinceD(G)issymmetric,itseigenvaluesareallrea1.Inaddition
5、,asD(G)isnonnegativeandirreducible,byPerron—FrobeniustheoremIthespectralradiusp(G)ofD(G)(calledthedistancespectralradiusofG),isexactlythelargesteigenvalueofD(C)withmultiplicityone;andthereexistsaunique(uptoamultiple)positiveeigenvectorcorrespondingtothiseigenvalue,usu
6、allyreferredtothePerronvectorofD(G).Thedistancematrixisveryusefu1indiferentfieldsincludingthedesignofcommunica-tionnetworks[1],graphembeddingtheory[2-4]aswellasmolecularstability[5,6].Balabaneta1.[7]proposedtheuseofthedistancespectralradiusasamoleculardescriptor.Gutma
7、neta1.『8]usedthedistancespectralradiustoinfertheextentofbranchingandmode1boilingpointsofanalkane.Therefore,maximizingorminimizingthedistancespectralradiusoveragivenclassofgraphsisofgreatinterestandsignificance.Recently,themaximalortheReceiveddate:2013—04—13Accepteddat
8、e-"2013—06—13Foundationitern:SupportedbyNationalNaturalScienceFoundationofChina(11071002);ProgramforNewCenturyExcellentTalen