简介:Wefirstapplynon-negativematrixtheorytothematrixK=D+A,whereDandAarethedegree-diagonalandadjacencymatricesofagraphG,respectively,toestablisharelationonthelargestLaplacianeigenvalueλ1(G)ofGandthespectralradiusp(K)ofK.Andthenbyusingthisrelationwepresenttwoupperboundsforλ1(G)anddeterminetheextremalgraphswhichachievetheupperbounds.