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Research on spectral Turán problems under coexistence constraints of matching and color-critical graphs
Natural Science of Hainan University 2026, 44(4): 451-457
Published: 25 August 2026
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This paper investigates the spectral Turán problem for graphs simultaneously excluding a matching Ms+1 of size s+1 and a color-critical graph F with chromatic number r+1. By introducing combinatorial parameters such as the covering number and independent covering number of the graph, this paper develops a unified framework for analyzing spectral extremal problems of degenerate forbidden graph families. Based on this framework, it is proved that, for sufficiently large s, the maximum spectral radius of an n-vertex {Ms+1,F}-free graph is attained by the complete r-partite graph G(n,r,s), and this extremal graph is uniquely determined. This result not only extends the edge-extremal results of Alon and Frankl to the spectral setting, but also completely determines the spectral extremal structure under the coexistence constraints of matchings and color-critical graphs in this setting.

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