ProjectedGradientMethodsforNon-negativeMatrixFactorizationChih-JenLinDepartmentofComputerScienceAbstractNon-negativematrixfactorization(NMF)canbeformulatedasaminimizationproblemwithboundconstraints.Althoughbound-constrainedoptimizationhasbeenstudiedextensivelyinboththeoryandpractice,sofarno