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- 93 pages, 2 figures. Comments and suggestions are welcome
AI中文摘要
设$G$是一个有$n$个顶点的简单连通图,令$\lambda_1(G),\lambda_2(G),\ldots,\lambda_n(G)$为其邻接矩阵$A(G)$的特征值。对于$p>0$,定义$G$的$p$-能量为$\mathcal E_p(G)=\sum_{i=1}^n |\lambda_i(G)|^p$。我们证明,对于每一个实数$p\geq2$和每一个有$n$个顶点的简单连通图$G$,有$\mathcal E_p(G)\geq\mathcal E_p(P_n)$,其中$P_n$表示有$n$个顶点的路径图。此外,对于每个固定的$p>2$,当且仅当$G\cong P_n$时取等号。结合已知的星形极小性结果,这完成了Nikiforov提出的两个问题的解答。证明结合了两种不同的比较原理。对于$2<p<4$,我们使用二分图的还原、分数幂的 Mellin 表示以及涉及匹配生成多项式和树转移的行列式比较。对于$p\geq4$,我们证明了二分图平方奇异值的二次止损比较,该比较通过秩一谱移估计、删除极小反例和终端稀疏太阳配置的有限认证分析来建立。作为应用,我们获得了正$p$-能量在若干情况下的路径极小性结果,以及拉普拉斯矩阵和无向拉普拉斯矩阵幂和及相关指标的结果。
英文摘要
Let $G$ be a simple connected graph on $n$ vertices, and let $λ_1(G),λ_2(G),\ldots,λ_n(G)$ be the eigenvalues of its adjacency matrix $A(G)$. For $p>0$, define the $p$-energy of $G$ by $\mathcal E_p(G)=\sum_{i=1}^n |λ_i(G)|^p$. We prove that, for every real number $p\ge 2$ and every simple connected graph $G$ on $n$ vertices, $$ \mathcal E_p(G)\ge \mathcal E_p(P_n), $$ where $P_n$ denotes the path on $n$ vertices. Moreover, for each fixed $p>2$, equality holds if and only if $G\cong P_n$. Together with the previously known star-minimality results, this completes the solution of two questions of Nikiforov.
The proof combines two different comparison principles. For $2<p<4$, we use a bipartite reduction, a Mellin representation of fractional powers, and a determinant comparison involving matching generating polynomials and tree shifts. For $p\ge4$, we prove a second-order stop-loss comparison for the squared singular values of bipartite graphs. This comparison is established by rank-one spectral-shift estimates, deletion-minimal counterexamples, and a finite certified analysis of the terminal sparse-sun configurations. As applications, we obtain sharp path-minimality results for positive $p$-energies in several cases, and for Laplacian and signless Laplacian power sums and related indices.