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MatrixFactorizationtechniquesforrecommendersystemsCataloguePaperBackgroundIntroductionRecommenderSystemsStrategiesMatrixFactorizationMethodsABasicMatrixFactorizationModelLearningAlgorithmAddingBiasesAddingInputSourcesTemporalDynamicsInputWithVaryingConfidenceLevelsNetflixPrizeCompetitionConclusionWednesday,April17,202421、PaperBackgroundWednesday,April17,202431.YehudaKoren,YahooResearch2.RobertBellandChrisVolinsky,AT&TLabs-Research3.PaperpublishedbytheIEEEComputerSocietyinAugust20094.AuthorwonthegrandNetflixPrizeCompetitioninSeptember20092、IntroductionModernconsumersareinundatedwithchoices.MoreretailorhavebecomeinterestedinRS,whichanalyzepatternsofuserinterestinproductstopridepersonalizedrecommendationsthatsuitauser'staste.NetflixandAhavemadeRSasalientpartoftheirwebsites.Particularlyuserfulforentainmentproductssuchasmovies,music,andTVshows.3、RecommenderSystemStrategiesContentFilteringCollaborativeFiltering
1.Neighborhoodmethods
user-oriented
item-oriented
2.LatentFatorModelWednesday,April17,202453.1、ContentsFilteringCreateaprofileforeachuserorproducttocharacterizeitsnature.Needtogatherexternalinformation.AknownsuccessfulrealizationofcontentfilteringistheMusicGenomeProject,whichisusedfortheInternetradioserviceP.Wednesday,April17,202463.2、CollaborativeFilteringAnalyzerelationshipsbetweenusersandinterdep-enciesamongproductstoidentifynewuser-itemas-Socitions.Disadvantages:coldstartTwoprimaryareas:neighborhoodmethodsuser-orienteditem-orientedLatentfactormodelsWednesday,April17,202473.2.1、NeighborhoodmethodsCenteredoncomputingtherelationshipsbetweenitemsor
users.Theitem-orientedapproachevaluatesa
user’spreferenceforanitembasedonratingsof“neighboring”itemsbythesameuser.Theuser-orientedapproachidentifieslike-mindeduserswhocancomplementeachother’sratings.Wednesday,April17,20248Example:3.2.2、LatentFactorModelsFindfeaturesthatdescribethecharacteristicsofratedobjects.Itemcharacteristicsanduserpreferencesaredescribedwithnumericalfactorvalues.Assumption:Ratingscanbeinferredfromamodelputtogetherfromasmallernumberofparameters.Wednesday,April17,2024104、MatrixFactorizationMethodsCharacterizebothitemsandusersbyvectorsoffactorsinferredfromitemratingpatterns.RSrelyondifferenttypesofinputdata.Strength:incorporationofadditionalinformation,implicitfeedback.Implicitfeedback:purchasehistory,browsinghistory,searchpatterns,mousemovementandsoon.Wednesday,April17,2024115、ABasicMatrixFactorizationModelDotproductcapturestheuser’sestimatedinterestintheitem:(1)Here,theelementsofmeasuretheextenttowhichtheitempossessesthosefactors,theelementsofmeasuretheextentofinteresttheuserhasinitemsthatarehighonthecorrespondingfactors.Challenge:Howtocomputeamappingofitemsandusersfactorvectors?Approaches:SingularValueDecompositionn(SVD)
Wednesday,April17,2024125.1、SingularValueDecompositionRequirefactoringtheuser-itemratingmatrixConventionalSVDisundefinedforincompleteImputationtofillinmissingvaluesIncreasestheamountofdataModelingdirectlytheobservedratingsWeneedtoapproachthatcansimplyignoremissingvalue
5.1、SingularValueDecompositionMeasures:aregularizedmodel(2)Here,isthesetofthe(u,i)pairsforwhichisknown(thetrainingset);theconstantcontrolstheextentofregularization,determinedbycross-validation.6、LearningAlgorithmsTwomethodstominizingEquation(2)
StochasticGradientDescent
AlteringLeastSquaresWednesday,April17,2024156.1、StochasticGradientDescentLoopthroughallratingsinthetrainingsetForeachgiventraingcase,thesystempredictsandcomputestheassociatedpredictionerrorBymagnitudeproportionaltointheoppositedirectionofthegradient
6.2、AlternatingLeastSquaresALSteachniquesrotatebetweenfixingtheandfixingtheALSisfavorableinatleasttwocases:AllowsmassiveparallelizationCenteredonimplicitdata
7、AddingBiasesAfirst-orderapproximationofthebiasinvolvedinratingisasfollows:(3)Here,istheoverallaverage;theparameters,indicatetheobserveddeviationsofuseranditemi.Includingbiasparametersintheprediction:(4)Optimize:(5)Wednesday,April17,2024188、AddingInputSourcesProblem:coldstartSolution:incorporateadditionalsourcesofinformationabouttheusers.Twoinformation:itemattributes,userattributesItemattribute:NormalizingthesumUserattribute:Optimaion:(6)
9、TemporalDynamicsRatingmaybeaffectedbytemporaleffectsPopularityofanitemmaychangeUser'sidentityandpreferencesmaychangeModelingtemporalaffectscanimporveaccuracysignificantlyRatingpredictionsasafunctionoftime:
(7)Wednesday,April17,20242010、InputwithVaringConfidencelevelsInseveralsetups,notallobservedratingsdeservethesameweightorconfidence.Plan:ConfidenceinobservingisdenotedasCostfounction:
(8)
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