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Distance signless Laplacian spectral radius for the existence of path-factors in graphs

  • Sizhong Zhou,
  • Zhiren Sun,
  • Hongxia Liu

摘要

Let G be a connected graph of order n, where n is a positive integer. A spanning subgraph F of G is called a path-factor if every component of F is a path of order at least 2. A \(P_{\ge k}\) P k -factor means a path-factor in which every component admits order at least k ( \(k\ge 2\) k 2 ). The distance matrix \({\mathcal {D}}(G)\) D ( G ) of G is an \(n\times n\) n × n real symmetric matrix whose (ij)-entry is the distance between the vertices \(v_i\) v i and \(v_j\) v j . The distance signless Laplacian matrix \({\mathcal {Q}}(G)\) Q ( G ) of G is defined by \({\mathcal {Q}}(G)=Tr(G)+{\mathcal {D}}(G)\) Q ( G ) = T r ( G ) + D ( G ) , where Tr(G) is the diagonal matrix of the vertex transmissions in G. The largest eigenvalue \(\eta _1(G)\) η 1 ( G ) of \({\mathcal {Q}}(G)\) Q ( G ) is called the distance signless Laplacian spectral radius of G. In this paper, we aim to present a distance signless Laplacian spectral radius condition to guarantee the existence of a \(P_{\ge 2}\) P 2 -factor in a graph and claim that the following statements are true: (i) G admits a \(P_{\ge 2}\) P 2 -factor for \(n\ge 4\) n 4 and \(n\ne 7\) n 7 if \(\eta _1(G)<\theta (n)\) η 1 ( G ) < θ ( n ) , where \(\theta (n)\) θ ( n ) is the largest root of the equation \(x^{3}-(5n-3)x^{2}+(8n^{2}-23n+48)x-4n^{3}+22n^{2}-74n+80=0\) x 3 - ( 5 n - 3 ) x 2 + ( 8 n 2 - 23 n + 48 ) x - 4 n 3 + 22 n 2 - 74 n + 80 = 0 ; (ii) G admits a \(P_{\ge 2}\) P 2 -factor for \(n=7\) n = 7 if \(\eta _1(G)<\frac{25+\sqrt{161}}{2}\) η 1 ( G ) < 25 + 161 2 .