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1、"*^YjUYdNAV(x)∈C(R,R),H(x,z)DzSZXn,Az:=(u,v),)
2、EliT>d(n.nÆ*~F;7;!;*;(C)cVX.ii"*^YjUYdAbstractThevariationalmethodisanapproximatecalculationmethodwhichbasedonthevariationalprinciple.Itisoneoftheimportantmethodsincomputationalmechanics,andaneffectiv
3、etooltosolvetheproblemofmechanicsandotherareas.ThestudyobjectofVariationalisextremumproblemofthefunctional.Thevariationalprinci-pleisavariationalformrepresentationsofphysicallaws,anditdoesnotcontainnewphysicalcontent.Itsvalueismainlyusedasthenewstartingpointforthestructure
4、ofclassicalmechanicstheory.Inotherwords,inallmotionstateofsatisfycertaincon-straints,actualmotionstateshouldmakesomephysicalquantitytheextremevalue.Inmechanics,optics,quantummechanicsandothersubjects,ithasthecorrespondingvariationalprinciple.Therearesomeimportantvariationa
5、lprinciplessuchasFermat’sprinciple,Hamiltonianprinciple,theprincipleofminimumenergyandminimumresid-ualenergyprinciple.Thevariationalmethodisapproximationcalculationmethodinthefieldofmechanics,physicsandotherdisciplines.Inthispaper,thedeformationofthefountaintheoremandfounta
6、intheorem,westudiedwithsuperlinearandasymptoticallylinearellipticequationsandsuperquadraicellipticsystemsandgivesomesufficientconditionsofexistencesofsolutions.Meanwhileweapplythemainresultstotheexistenceofsolutionsforboundaryvalueproblems.Thethesisisdividedintothreechapters
7、accordingtocontents.Inchapter1,itintroducetheoriginandsettingofvariationalmethod.Inchapter2,basedonavariantfountaintheoremestablishedbyW.Zou,westudythefollowingellipticboundaryvalueproblem−∆u=µf(x,u)inΩ,u=0on∂Ω,whereµ∈(0,∞),Ω⊂RN(N>2)isboundeddomainwithsmoothboundary,fisodd
8、inuandcontinuous.Forsuperlinearcase,insharpcontrasttotheexistingresultsintheliterature,wedonotmakethewell-knownAmbrosetti-Rabinowitztypetechnicalconditionnearinfinityandnotmakeanyassumptionsnearzeroonthebehaviorsofthenonlinearityf,weobtaintheexistenceandmultiplicityofsoluti
9、ons.Wealsoconsiderthesituationwherefisasymptoticallylinearwithassumptionsdifferentfromthos