<p>The distance Laplacian matrix of a connected graph <i>G</i> is defined by <InlineEquation ID="IEq1"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="40314_2025_3095_Article_IEq1.gif" Format="GIF" Height="21" Rendition="HTML" Resolution="72" Type="Linedraw" Width="179" /> </InlineMediaObject> <EquationSource Format="TEX">\({D^L}(G)=Tr(G)-D(G)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msup> <mi>D</mi> <mi>L</mi> </msup> <mrow> <mo stretchy="false">(</mo> <mi>G</mi> <mo stretchy="false">)</mo> </mrow> <mo>=</mo> <mi>T</mi> <mi>r</mi> <mrow> <mo stretchy="false">(</mo> <mi>G</mi> <mo stretchy="false">)</mo> </mrow> <mo>-</mo> <mi>D</mi> <mrow> <mo stretchy="false">(</mo> <mi>G</mi> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation>, where <InlineEquation ID="IEq2"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="40314_2025_3095_Article_IEq2.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="50" /> </InlineMediaObject> <EquationSource Format="TEX">\(Tr\left( G\right) \)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>T</mi> <mi>r</mi> <mfenced close=")" open="("> <mi>G</mi> </mfenced> </mrow> </math></EquationSource> </InlineEquation> is the diagonal matrix with vertex transmissions of <i>G</i> and <InlineEquation ID="IEq3"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="40314_2025_3095_Article_IEq3.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="45" /> </InlineMediaObject> <EquationSource Format="TEX">\(D\left( G\right) \)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>D</mi> <mfenced close=")" open="("> <mi>G</mi> </mfenced> </mrow> </math></EquationSource> </InlineEquation> is the distance matrix of <i>G</i>. The distance Laplacian eigenvalues of <i>G</i> are denoted by <InlineEquation ID="IEq4"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="40314_2025_3095_Article_IEq4.gif" Format="GIF" Height="22" Rendition="HTML" Resolution="72" Type="Linedraw" Width="244" /> </InlineMediaObject> <EquationSource Format="TEX">\({\partial _n^L\left( G\right) }\le {\partial _{n-1}^L\left( G\right) }\le \cdots \le {\partial _1^L\left( G\right) }\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mrow> <msubsup> <mi>∂</mi> <mi>n</mi> <mi>L</mi> </msubsup> <mfenced close=")" open="("> <mi>G</mi> </mfenced> </mrow> <mo>≤</mo> <mrow> <msubsup> <mi>∂</mi> <mrow> <mi>n</mi> <mo>-</mo> <mn>1</mn> </mrow> <mi>L</mi> </msubsup> <mfenced close=")" open="("> <mi>G</mi> </mfenced> </mrow> <mo>≤</mo> <mo>⋯</mo> <mo>≤</mo> <mrow> <msubsup> <mi>∂</mi> <mn>1</mn> <mi>L</mi> </msubsup> <mfenced close=")" open="("> <mi>G</mi> </mfenced> </mrow> </mrow> </math></EquationSource> </InlineEquation>. For a connected graph <i>G</i> with order <i>n</i> and size <i>m</i>, we denote by <InlineEquation ID="IEq5"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="40314_2025_3095_Article_IEq5.gif" Format="GIF" Height="21" Rendition="HTML" Resolution="72" Type="Linedraw" Width="224" /> </InlineMediaObject> <EquationSource Format="TEX">\({U_k}\left( G\right) =\partial _1^L\left( G\right) +\cdots +\partial _k^L\left( G\right) \)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>U</mi> <mi>k</mi> </msub> <mfenced close=")" open="("> <mi>G</mi> </mfenced> <mo>=</mo> <msubsup> <mi>∂</mi> <mn>1</mn> <mi>L</mi> </msubsup> <mfenced close=")" open="("> <mi>G</mi> </mfenced> <mo>+</mo> <mo>⋯</mo> <mo>+</mo> <msubsup> <mi>∂</mi> <mi>k</mi> <mi>L</mi> </msubsup> <mfenced close=")" open="("> <mi>G</mi> </mfenced> </mrow> </math></EquationSource> </InlineEquation> the sum of <i>k</i> largest distance Laplacian eigenvalues of <i>G</i>. In this paper, we firstly obtain a relation between the sum of the distance Laplacian eigenvalues of the graph <i>G</i> and the sum of the Laplacian eigenvalues of the complement <InlineEquation ID="IEq6"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="40314_2025_3095_Article_IEq6.gif" Format="GIF" Height="17" Rendition="HTML" Resolution="72" Type="Linedraw" Width="18" /> </InlineMediaObject> <EquationSource Format="TEX">\(\overline{G}\)</EquationSource> <EquationSource Format="MATHML"><math> <mover> <mi>G</mi> <mo>¯</mo> </mover> </math></EquationSource> </InlineEquation> of <i>G</i>. Then we show that graphs of diameter one and connected graphs of diameter 2 with given large maximum degree for all <i>k</i> satisfy <InlineEquation ID="IEq7"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="40314_2025_3095_Article_IEq7.gif" Format="GIF" Height="43" Rendition="HTML" Resolution="72" Type="Linedraw" Width="213" /> </InlineMediaObject> <EquationSource Format="TEX">\(U_k(G) \le W(G)+\left( {\begin{array}{c}k+2\\ 3\end{array}}\right) ,\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msub> <mi>U</mi> <mi>k</mi> </msub> <mrow> <mo stretchy="false">(</mo> <mi>G</mi> <mo stretchy="false">)</mo> </mrow> <mo>≤</mo> <mi>W</mi> <mrow> <mo stretchy="false">(</mo> <mi>G</mi> <mo stretchy="false">)</mo> </mrow> <mo>+</mo> <mfenced close=")" open="("> <mrow> <mtable> <mtr> <mtd> <mrow> <mi>k</mi> <mo>+</mo> <mn>2</mn> </mrow> </mtd> </mtr> <mtr> <mtd> <mrow> <mrow /> <mn>3</mn> </mrow> </mtd> </mtr> </mtable> </mrow> </mfenced> <mo>,</mo> </mrow> </math></EquationSource> </InlineEquation> where <i>W</i>(<i>G</i>) is the transmission (or Wiener index) of <i>G</i>.</p>

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Brouwer type conjecture for the eigenvalues of distance Laplacian matrix of a graph

  • Yuwei Zhou,
  • Ligong Wang,
  • Yirui Chai

摘要

The distance Laplacian matrix of a connected graph G is defined by \({D^L}(G)=Tr(G)-D(G)\) D L ( G ) = T r ( G ) - D ( G ) , where \(Tr\left( G\right) \) T r G is the diagonal matrix with vertex transmissions of G and \(D\left( G\right) \) D G is the distance matrix of G. The distance Laplacian eigenvalues of G are denoted by \({\partial _n^L\left( G\right) }\le {\partial _{n-1}^L\left( G\right) }\le \cdots \le {\partial _1^L\left( G\right) }\) n L G n - 1 L G 1 L G . For a connected graph G with order n and size m, we denote by \({U_k}\left( G\right) =\partial _1^L\left( G\right) +\cdots +\partial _k^L\left( G\right) \) U k G = 1 L G + + k L G the sum of k largest distance Laplacian eigenvalues of G. In this paper, we firstly obtain a relation between the sum of the distance Laplacian eigenvalues of the graph G and the sum of the Laplacian eigenvalues of the complement \(\overline{G}\) G ¯ of G. Then we show that graphs of diameter one and connected graphs of diameter 2 with given large maximum degree for all k satisfy \(U_k(G) \le W(G)+\left( {\begin{array}{c}k+2\\ 3\end{array}}\right) ,\) U k ( G ) W ( G ) + k + 2 3 , where W(G) is the transmission (or Wiener index) of G.