Let G be a simple graph with vertex set V(G) and edge set E(G) .Denote the sum of the first k Laplacian eigenvalues of graph G by Sk (G) .Brouwer et al .proposed a conjecture that Sk (G)≤ e(G)+ (k+12 ) ,where 1≤ k≤ n ,for any simple graph G .In this pa-per ,we give a new upper bound of Sk (T) and prove the conjecture holds in the cases of unicyclic and bicyclic graphs when k≠3 .%设 G是一个顶点集为V(G),边集为 E(G)的简单图。 Sk (G)表示图 G的拉普拉斯特征值的前k项部分和。Brouwer等给出如下猜想:Sk (G)≤ e(G)+(k+12),1≤ k≤ n。此文给出了一类树 T的Sk (T)新的上界,并证明在单圈图,双圈图(k≠3)的情形下猜想也是成立的。
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