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一类下降非线性共轭梯度法 Abstract: Nonlinearconjugategradient(NCG)methodsarewidelyusedinoptimizationproblemswithlargesearchspaces.However,traditionalNCGmethodsoftensufferfromconvergencedifficulties,especiallywhendealingwithnon-lineardescentproblems.Inordertoovercometheseproblems,down-conversionalgorithmswereintroduced,whichallowedforfasterconvergenceandbetteroptimizationresults.Thispaperaimstoprovideanoverviewofthedown-conversionnonlinearconjugategradientmethod,discussingitsadvantagesandlimitations,andcomparingittootheroptimizationmethods.Thepaperalsointroducessomeofthemostimportantapplicationsofthemethodinthefieldofmachinelearning. Introduction: Optimizationproblemsariseinmanyfieldsofscienceandengineering,includingmachinelearning,computervision,operationsresearch,andfinance.Intryingtosolvethesecomplexproblems,acommondifficultyisthatthesearchspaceisoftensolargeandcomplexthatitishardtofindanoptimalsolutionthroughbrute-forcemethods.Therefore,optimizationmethodsareoftenusedtoefficientlyexplorethesearchspaceandfindaglobalorlocalminimum. Nonlinearconjugategradient(NCG)methodsareatypeofoptimizationmethodthathasbeenwidelyusedinrecentyears.ThebasicideabehindNCGistoiterativelysearchfortheoptimaldirectionbycombiningaconjugategradientmethodwithalinesearchmethod.Theconjugategradientmethodensuresthatthesearchdirectionisorthogonaltoallprevioussearchdirections,whilethelinesearchmethodtriestofindthestepsizethatleadstothemaximalreductionoftheobjectivefunction. However,traditionalNCGmethodsoftenhaveconvergencedifficulties,especiallywhenappliedtonon-lineardescentproblems.Toaddressthisproblem,anewclassofdown-conversionNCGalgorithmshavebeenproposed,whichallowforfasterconvergenceandbetteroptimizationresults.Thispaperprovidesacomprehensiveanalysisofthedown-conversionNCGmethod,discussingitsadvantagesandlimitations,andcomparingittootheroptimizationmethods. TheDown-ConversionNonlinearConjugateGradientMethod: Thebasicideabehindthedown-conversionNCGmethodistooptimizetheobjectivefunctionbyiterativelyreduci