沙漏图是在一条路的两个悬挂点上各粘上一个三角形而形成的图.对于一个图G,若没有其他非同构的图和它是L-同谱的或Q-同谱的,则它是由L-谱,或Q-谱唯一确定的(G简记为DLS或DQS).将利用讨论排除的方法来证明沙漏图的线图是由它的(无符号)拉普拉斯谱唯一确定的.
A sandglass graph is a graph obtained by appending a triangle to each pendant vertex of a path.A graph Gis said to be determined by its L-spectrum(or Q-spectrum)if there is no other non-isomorphic graph L-cospectral(or Q-cospectral)with it,denoted by DLS(or DQS).In this paper,using discussion and exclusion,we show that the line graphs of sandglass graphs are determined by their Laplacian spectra as well as their signless Laplacian spectra.