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匹配与色临界图共存约束下的谱Turán问题研究

Research on spectral Turán problems under coexistence constraints of matching and color-critical graphs

  • 摘要: 研究了同时禁止大小为 s+1 的匹配 M_s+1 和色数为 r+1 的色临界图 F 的谱Turán问题。通过引入图的覆盖数与独立覆盖数等组合参数,建立了一个分析退化图族谱极值的理论框架。在此框架下,证明了当 s 充分大时, n 阶 \M_s+1,F\\text-free 图的最大谱半径由完全 r 部图 G(n,r,s) 达到,且该极值图是唯一的。该结果不仅将Alon和Frankl关于边极值的结果推广到谱情形,也为匹配与色临界图共存约束下的谱极值问题提供了完整解答。

     

    Abstract: This paper studies the spectral Turán problems for simultaneously prohibiting the matching M_s+1 of size s+1 and the chromatic critical graph F with chromatic number r+1 . By introducing combinatorial parameters such as the covering number and independent covering number of the graph, we establish a theoretical framework for analyzing the spectral extremal values of degenerate graph families. Under this framework, we prove that when s is sufficiently large, the maximum spectral radius of an n -order \M_s+1,F\\text-free graph reaches the complete r -partite graph G(n,r,s) , and this extremal graph is unique. This result not only extends the results of Alon and Frankl on edge extremal values to the spectral case, but also provides a complete solution to the spectral extremal value problem under the constraint of the coexistence of matchings and chromatic critical graphs.

     

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