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On eigenvalues of Seidel matrices and Haemers' conjecture

机译:关于Seidel矩阵的特征值和Haemers猜想

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For a graph G, let S(G) be the Seidel matrix of G and theta(1)(G),...,theta(n)(G) be the eigenvalues of S(G). The Seidel energy of G is defined as |theta(1)(G)|+ ... +|theta n(G)|. Willem Haemers conjectured that the Seidel energy of any graph with n vertices is at least 2n - 2, the Seidel energy of the complete graph with n vertices. Motivated by this conjecture, we prove that for any alpha with 0 < alpha < 2, |theta(1)(G)|(alpha) + ... + |theta(n)(G)|(alpha) >= (n - 1)(alpha) + n - 1 if and only if |det S(G)| >= n - 1. This, in particular, implies the Haemers' conjecture for all graphs G with |det S(G)| >= n - 1. A computation on the fraction of graphs with | det S(G)| < n - 1 is reported. Motivated by that, we conjecture that almost all graphs G of order n satisfy | det S(G)| >= n - 1. In connection with this conjecture, we note that almost all graphs of order n have a Seidel energy of order Theta (n(3/2)). Finally, we prove that self-complementary graphs G of order n = 1 (mod 4) have det S(G) = 0.
机译:对于图G,令S(G)为G的赛德尔矩阵,theta(1)(G),...,theta(n)(G)为S(G)的特征值。 G的赛德尔能量定义为| theta(1)(G)| + ... + | then n(G)|。威廉·海默斯(Willem Haemers)推测,具有n个顶点的任何图的赛德尔能量至少为2n-2,即具有n个顶点的完整图的赛德尔能量。受此推测的启发,我们证明对于0 = n-1。尤其是,这意味着所有具有| det S(G)|的图G的Haemers猜想。 > = n-1.用| |计算图的分数det S(G)|报告 = n-1。关于这个猜想,我们注意到几乎所有n阶的图都有塞塔能级Theta(n(3/2))。最后,我们证明阶数为n = 1(模4)的自补图G的det S(G)= 0。

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