具有五个不同于0和1的Laplacian特征值的单圈图

设$U$是$n$阶单圈图, $m_{U}(1)$是$U$的拉普拉斯特征值1的重数.众所周知,0是连通图重数为1的拉普拉斯特征值.这意味着如果$U$有五个不同于0和1的拉普拉斯特征值,那么$m_U(1)=n-6$.本文完整刻画了$m_U(1)=n-6$的所有单圈图.     

图的剖分点-边冠运算下的规范拉普拉斯谱

A subdivision vertex-edge corona G_1~S?(∪ G_3~E) is a graph that consists of S(G_1),|V(G_1)| copies of G_2 and |I(G_1)| copies of G_3 by joining the i-th vertex in V(G_1) to each vertex in the i-th copy of G_2 and i-th vertex of I(G_1) to each vertex in the i-th copy of G_3.In this paper, we determine the normalized Laplacian spectrum of G_1~S?(G_2~V∪ G_3~E) in terms of the corresponding normalized Laplacian spectra of three connected regular graphs G_1, G_2 and G_3. As applications, we construct some non-regular normalized Laplacian cospectral graphs. In addition, we also give the multiplicative degree-Kirchhoff index, the Kemeny's constant and the number of the spanning trees of G_1~S?(G_2~V∪ G_3~E) on three regular graphs.