<p>Let <i>G</i> be a simple connected simple graph of order <i>n</i>. The distance Laplacian matrix <InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(D^{L}(G)\)</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> </mrow> </math></EquationSource> </InlineEquation> is defined as <InlineEquation ID="IEq2"> <EquationSource Format="TEX">\(D^L(G)=Diag(Tr)-D(G)\)</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>D</mi> <mi>i</mi> <mi>a</mi> <mi>g</mi> <mrow> <mo stretchy="false">(</mo> <mi>T</mi> <mi>r</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 <i>Diag</i>(<i>Tr</i>) is the diagonal matrix of vertex transmissions and <i>D</i>(<i>G</i>) is the distance matrix of <i>G</i>. The eigenvalues of <InlineEquation ID="IEq3"> <EquationSource Format="TEX">\(D^{L}(G)\)</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> </mrow> </math></EquationSource> </InlineEquation> are the distance Laplacian eigenvalues of <i>G</i> and are denoted by <InlineEquation ID="IEq4"> <EquationSource Format="TEX">\(\partial _{1}^{L}(G), \partial _{2}^{L}(G),\dots ,\partial _{n}^{L}(G)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msubsup> <mi>∂</mi> <mrow> <mn>1</mn> </mrow> <mi>L</mi> </msubsup> <mrow> <mo stretchy="false">(</mo> <mi>G</mi> <mo stretchy="false">)</mo> </mrow> <mo>,</mo> <msubsup> <mi>∂</mi> <mrow> <mn>2</mn> </mrow> <mi>L</mi> </msubsup> <mrow> <mo stretchy="false">(</mo> <mi>G</mi> <mo stretchy="false">)</mo> </mrow> <mo>,</mo> <mo>⋯</mo> <mo>,</mo> <msubsup> <mi>∂</mi> <mrow> <mi>n</mi> </mrow> <mi>L</mi> </msubsup> <mrow> <mo stretchy="false">(</mo> <mi>G</mi> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation>. The <i> distance Laplacian spread</i> <i>DLS</i>(<i>G</i>) of a connected graph <i>G</i> is the difference between largest and second smallest distance Laplacian eigenvalues, that is, <InlineEquation ID="IEq5"> <EquationSource Format="TEX">\(\partial _{1}^{L}(G)-\partial _{n-1}^{L}(G)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msubsup> <mi>∂</mi> <mrow> <mn>1</mn> </mrow> <mi>L</mi> </msubsup> <mrow> <mo stretchy="false">(</mo> <mi>G</mi> <mo stretchy="false">)</mo> </mrow> <mo>-</mo> <msubsup> <mi>∂</mi> <mrow> <mi>n</mi> <mo>-</mo> <mn>1</mn> </mrow> <mi>L</mi> </msubsup> <mrow> <mo stretchy="false">(</mo> <mi>G</mi> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation>. We obtain bounds for <i>DLS</i>(<i>G</i>) in terms of the Wiener index <i>W</i>(<i>G</i>), order <i>n</i> and the maximum transmission degree <InlineEquation ID="IEq6"> <EquationSource Format="TEX">\(Tr_{max}(G)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>T</mi> <msub> <mi>r</mi> <mrow> <mi mathvariant="italic">max</mi> </mrow> </msub> <mrow> <mo stretchy="false">(</mo> <mi>G</mi> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> of <i>G</i> and characterize the extremal graphs. We obtain two lower bounds for <i>DLS</i>(<i>G</i>), the first one in terms of the order, diameter and the Wiener index of the graph, and the second one in terms of the order, maximum degree and the independence number of the graph. For a connected <i>k</i>-partite graph <i>G</i>, <InlineEquation ID="IEq7"> <EquationSource Format="TEX">\(k\le n-1\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>k</mi> <mo>≤</mo> <mi>n</mi> <mo>-</mo> <mn>1</mn> </mrow> </math></EquationSource> </InlineEquation>, with <i>n</i> vertices having disconnected complement, we show that <InlineEquation ID="IEq8"> <EquationSource Format="TEX">\( DLS(G)\ge \Big \lfloor \frac{n}{k}\Big \rfloor \)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>D</mi> <mi>L</mi> <mi>S</mi> <mrow> <mo stretchy="false">(</mo> <mi>G</mi> <mo stretchy="false">)</mo> </mrow> <mo>≥</mo> <mrow> <mo maxsize="1.623em" minsize="1.623em" stretchy="true">⌊</mo> </mrow> <mfrac> <mi>n</mi> <mi>k</mi> </mfrac> <mrow> <mo maxsize="1.623em" minsize="1.623em" stretchy="true">⌋</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> with equality if and only if <i>G</i> is a complete balanced <i>k</i>-partite graph.</p>

错误:搜索内容不能为空,请输入英文关键词
错误:关键词超出字数限制,请精简
高级检索

On Distance Laplacian Spread, Wiener Index and Independence Number of a Graph

  • Saleem Khan,
  • S. Pirzada

摘要

Let G be a simple connected simple graph of order n. The distance Laplacian matrix \(D^{L}(G)\) D L ( G ) is defined as \(D^L(G)=Diag(Tr)-D(G)\) D L ( G ) = D i a g ( T r ) - D ( G ) , where Diag(Tr) is the diagonal matrix of vertex transmissions and D(G) is the distance matrix of G. The eigenvalues of \(D^{L}(G)\) D L ( G ) are the distance Laplacian eigenvalues of G and are denoted by \(\partial _{1}^{L}(G), \partial _{2}^{L}(G),\dots ,\partial _{n}^{L}(G)\) 1 L ( G ) , 2 L ( G ) , , n L ( G ) . The distance Laplacian spread DLS(G) of a connected graph G is the difference between largest and second smallest distance Laplacian eigenvalues, that is, \(\partial _{1}^{L}(G)-\partial _{n-1}^{L}(G)\) 1 L ( G ) - n - 1 L ( G ) . We obtain bounds for DLS(G) in terms of the Wiener index W(G), order n and the maximum transmission degree \(Tr_{max}(G)\) T r max ( G ) of G and characterize the extremal graphs. We obtain two lower bounds for DLS(G), the first one in terms of the order, diameter and the Wiener index of the graph, and the second one in terms of the order, maximum degree and the independence number of the graph. For a connected k-partite graph G, \(k\le n-1\) k n - 1 , with n vertices having disconnected complement, we show that \( DLS(G)\ge \Big \lfloor \frac{n}{k}\Big \rfloor \) D L S ( G ) n k with equality if and only if G is a complete balanced k-partite graph.