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1、AGENERALFRAMEWORKFORACLASSOFFIRSTORDERPRIMAL-DUALALGORITHMSFORCONVEXOPTIMIZATIONINIMAGINGSCIENCEERNIEESSERXIAOQUNZHANGTONYCHANAbstract.Wegeneralizetheprimal-dualhybridgradient(PDHG)algorithmproposedbyZhuandChanin[M.Zhu,andT.F.Chan,AnEfficientPrimal-DualHybrid
2、GradientAlgorithmforTotalVariationImageRestoration,UCLACAMReport[08-34],May2008],explainconnectionstosimilarmethodsanddiscussconvergenceofseveralspecialcasesandmodifications.Inparticular,wepointoutaconvergenceresultforamodifiedversionofPDHGthathasasimilarlygo
3、odempiricalconvergenceratefortotalvariation(TV)minimizationproblems.Itsconvergencefollowsfromin-terpretingitasaninexactUzawamethod.WealsoproveaconvergenceresultforPDHGappliedtoTVdenoisingwithsomerestrictionsonthePDHGstepsizeparameters.Itisshownhowtointerpre
4、tthisspecialcaseasaprojectedaveragedgradientmethodappliedtothedualfunctional.WediscusstherangeofparametersforwhichtheinexactUzawamethodandtheprojectedaveragedgradientmethodcanbeshowntoconverge.WealsopresentsomenumericalcomparisonsofthesealgorithmsappliedtoT
5、Vdenoising,TVdeblurringandconstrainedl1minimizationproblems.Keywords.convexoptimization,totalvariationminimization,primal-dualmethods,operatorsplitting,l1basispursuitAMSsubjectclassifications.90C25,90C06,49K35,49N45,65K101.Introduction.Totalvariationminimiza
6、tionproblemsariseinmanyimageprocessingapplicationsforregularizinginverseproblemswhereoneexpectsthere-coveredimageorsignaltobepiecewiseconstantorhavesparsegradient.However,alackofdifferentiabilitymakesminimizingTVregularizedfunctionalscomputationallychallengi
7、ng,andsothereisconsiderableinterestinefficientalgorithms,especiallyforlargescaleproblems.Moregenerally,thereisinterestinpracticalmethodsforsolvingnon-differentiableconvexoptimizationproblems,TVminimizationbeinganimportantspecialcase.ThePDHGalgorithm[57]inagene
8、ralsettingisamethodforsolvingproblemsoftheformminJ(Au)+H(u),u∈RmwhereJandHareclosedproperconvexfunctionsandA∈Rn×m.Usually,J(Au)willcorrespondtoaregularizingtermoftheformkAuk,inwhichcasethePDHGmethodwor