部分立方体的立方多项式与其交叉图的小块多项式之间的关系

IF 0.9 3区 数学 Q2 MATHEMATICS
Yan-Ting Xie, Yong-De Feng, Shou-Jun Xu
{"title":"部分立方体的立方多项式与其交叉图的小块多项式之间的关系","authors":"Yan-Ting Xie,&nbsp;Yong-De Feng,&nbsp;Shou-Jun Xu","doi":"10.1002/jgt.23099","DOIUrl":null,"url":null,"abstract":"<p>Partial cubes are the graphs which can be embedded into hypercubes. The <i>cube polynomial</i> of a graph <span></span><math>\n \n <mrow>\n <mi>G</mi>\n </mrow></math> is a counting polynomial of induced hypercubes of <span></span><math>\n \n <mrow>\n <mi>G</mi>\n </mrow></math>, which is defined as <span></span><math>\n \n <mrow>\n <mi>C</mi>\n \n <mrow>\n <mo>(</mo>\n \n <mrow>\n <mi>G</mi>\n \n <mo>,</mo>\n \n <mi>x</mi>\n </mrow>\n \n <mo>)</mo>\n </mrow>\n \n <mo>≔</mo>\n \n <msub>\n <mo>∑</mo>\n \n <mrow>\n <mi>i</mi>\n \n <mo>⩾</mo>\n \n <mn>0</mn>\n </mrow>\n </msub>\n \n <msub>\n <mi>α</mi>\n \n <mi>i</mi>\n </msub>\n \n <mrow>\n <mo>(</mo>\n \n <mi>G</mi>\n \n <mo>)</mo>\n </mrow>\n \n <msup>\n <mi>x</mi>\n \n <mi>i</mi>\n </msup>\n </mrow></math>, where <span></span><math>\n \n <mrow>\n <msub>\n <mi>α</mi>\n \n <mi>i</mi>\n </msub>\n \n <mrow>\n <mo>(</mo>\n \n <mi>G</mi>\n \n <mo>)</mo>\n </mrow>\n </mrow></math> is the number of induced <span></span><math>\n \n <mrow>\n <mi>i</mi>\n </mrow></math>-cubes (hypercubes of dimension <span></span><math>\n \n <mrow>\n <mi>i</mi>\n </mrow></math>) of <span></span><math>\n \n <mrow>\n <mi>G</mi>\n </mrow></math>. The <i>clique polynomial</i> of <span></span><math>\n \n <mrow>\n <mi>G</mi>\n </mrow></math> is defined as <span></span><math>\n \n <mrow>\n <mi>C</mi>\n \n <mi>l</mi>\n \n <mrow>\n <mo>(</mo>\n \n <mrow>\n <mi>G</mi>\n \n <mo>,</mo>\n \n <mi>x</mi>\n </mrow>\n \n <mo>)</mo>\n </mrow>\n \n <mo>≔</mo>\n \n <msub>\n <mo>∑</mo>\n \n <mrow>\n <mi>i</mi>\n \n <mo>⩾</mo>\n \n <mn>0</mn>\n </mrow>\n </msub>\n \n <msub>\n <mi>a</mi>\n \n <mi>i</mi>\n </msub>\n \n <mrow>\n <mo>(</mo>\n \n <mi>G</mi>\n \n <mo>)</mo>\n </mrow>\n \n <msup>\n <mi>x</mi>\n \n <mi>i</mi>\n </msup>\n </mrow></math>, where <span></span><math>\n \n <mrow>\n <msub>\n <mi>a</mi>\n \n <mi>i</mi>\n </msub>\n \n <mrow>\n <mo>(</mo>\n \n <mi>G</mi>\n \n <mo>)</mo>\n </mrow>\n </mrow></math> (<span></span><math>\n \n <mrow>\n <mi>i</mi>\n \n <mo>⩾</mo>\n \n <mn>1</mn>\n </mrow></math>) is the number of <span></span><math>\n \n <mrow>\n <mi>i</mi>\n </mrow></math>-cliques in <span></span><math>\n \n <mrow>\n <mi>G</mi>\n </mrow></math> and <span></span><math>\n \n <mrow>\n <msub>\n <mi>a</mi>\n \n <mn>0</mn>\n </msub>\n \n <mrow>\n <mo>(</mo>\n \n <mi>G</mi>\n \n <mo>)</mo>\n </mrow>\n \n <mo>=</mo>\n \n <mn>1</mn>\n </mrow></math>. Equivalently, <span></span><math>\n \n <mrow>\n <mi>C</mi>\n \n <mi>l</mi>\n \n <mrow>\n <mo>(</mo>\n \n <mrow>\n <mi>G</mi>\n \n <mo>,</mo>\n \n <mi>x</mi>\n </mrow>\n \n <mo>)</mo>\n </mrow>\n </mrow></math> is exactly the independence polynomial of the complement <span></span><math>\n \n <mrow>\n <mover>\n <mi>G</mi>\n \n <mo>¯</mo>\n </mover>\n </mrow></math> of <span></span><math>\n \n <mrow>\n <mi>G</mi>\n </mrow></math>. The <i>crossing graph</i> <span></span><math>\n \n <mrow>\n <msup>\n <mi>G</mi>\n \n <mi>#</mi>\n </msup>\n </mrow></math> of a partial cube <span></span><math>\n \n <mrow>\n <mi>G</mi>\n </mrow></math> is the graph whose vertices are corresponding to the <span></span><math>\n \n <mrow>\n <mi>Θ</mi>\n </mrow></math>-classes of <span></span><math>\n \n <mrow>\n <mi>G</mi>\n </mrow></math>, and two <span></span><math>\n \n <mrow>\n <mi>Θ</mi>\n </mrow></math>-classes are adjacent in <span></span><math>\n \n <mrow>\n <msup>\n <mi>G</mi>\n \n <mi>#</mi>\n </msup>\n </mrow></math> if and only if they cross in <span></span><math>\n \n <mrow>\n <mi>G</mi>\n </mrow></math>. In the present paper, we prove that for a partial cube <span></span><math>\n \n <mrow>\n <mi>G</mi>\n </mrow></math>, <span></span><math>\n \n <mrow>\n <mi>C</mi>\n \n <mrow>\n <mo>(</mo>\n \n <mrow>\n <mi>G</mi>\n \n <mo>,</mo>\n \n <mi>x</mi>\n </mrow>\n \n <mo>)</mo>\n </mrow>\n \n <mo>⩽</mo>\n \n <mi>C</mi>\n \n <mi>l</mi>\n \n <mrow>\n <mo>(</mo>\n \n <mrow>\n <msup>\n <mi>G</mi>\n \n <mi>#</mi>\n </msup>\n \n <mo>,</mo>\n \n <mi>x</mi>\n \n <mo>+</mo>\n \n <mn>1</mn>\n </mrow>\n \n <mo>)</mo>\n </mrow>\n </mrow></math> and the equality holds if and only if <span></span><math>\n \n <mrow>\n <mi>G</mi>\n </mrow></math> is a median graph. Since every graph can be represented as the crossing graph of a median graph, the above necessary-and-sufficient result shows that the study on the cube polynomials of median graphs can be transformed to the one on the clique polynomials of general graphs (equivalently, on the independence polynomials of their complements). In addition, we disprove the conjecture that the cube polynomials of median graphs are unimodal.</p>","PeriodicalId":16014,"journal":{"name":"Journal of Graph Theory","volume":"106 4","pages":"907-922"},"PeriodicalIF":0.9000,"publicationDate":"2024-04-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":"{\"title\":\"A relation between the cube polynomials of partial cubes and the clique polynomials of their crossing graphs\",\"authors\":\"Yan-Ting Xie,&nbsp;Yong-De Feng,&nbsp;Shou-Jun Xu\",\"doi\":\"10.1002/jgt.23099\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"<p>Partial cubes are the graphs which can be embedded into hypercubes. The <i>cube polynomial</i> of a graph <span></span><math>\\n \\n <mrow>\\n <mi>G</mi>\\n </mrow></math> is a counting polynomial of induced hypercubes of <span></span><math>\\n \\n <mrow>\\n <mi>G</mi>\\n </mrow></math>, which is defined as <span></span><math>\\n \\n <mrow>\\n <mi>C</mi>\\n \\n <mrow>\\n <mo>(</mo>\\n \\n <mrow>\\n <mi>G</mi>\\n \\n <mo>,</mo>\\n \\n <mi>x</mi>\\n </mrow>\\n \\n <mo>)</mo>\\n </mrow>\\n \\n <mo>≔</mo>\\n \\n <msub>\\n <mo>∑</mo>\\n \\n <mrow>\\n <mi>i</mi>\\n \\n <mo>⩾</mo>\\n \\n <mn>0</mn>\\n </mrow>\\n </msub>\\n \\n <msub>\\n <mi>α</mi>\\n \\n <mi>i</mi>\\n </msub>\\n \\n <mrow>\\n <mo>(</mo>\\n \\n <mi>G</mi>\\n \\n <mo>)</mo>\\n </mrow>\\n \\n <msup>\\n <mi>x</mi>\\n \\n <mi>i</mi>\\n </msup>\\n </mrow></math>, where <span></span><math>\\n \\n <mrow>\\n <msub>\\n <mi>α</mi>\\n \\n <mi>i</mi>\\n </msub>\\n \\n <mrow>\\n <mo>(</mo>\\n \\n <mi>G</mi>\\n \\n <mo>)</mo>\\n </mrow>\\n </mrow></math> is the number of induced <span></span><math>\\n \\n <mrow>\\n <mi>i</mi>\\n </mrow></math>-cubes (hypercubes of dimension <span></span><math>\\n \\n <mrow>\\n <mi>i</mi>\\n </mrow></math>) of <span></span><math>\\n \\n <mrow>\\n <mi>G</mi>\\n </mrow></math>. The <i>clique polynomial</i> of <span></span><math>\\n \\n <mrow>\\n <mi>G</mi>\\n </mrow></math> is defined as <span></span><math>\\n \\n <mrow>\\n <mi>C</mi>\\n \\n <mi>l</mi>\\n \\n <mrow>\\n <mo>(</mo>\\n \\n <mrow>\\n <mi>G</mi>\\n \\n <mo>,</mo>\\n \\n <mi>x</mi>\\n </mrow>\\n \\n <mo>)</mo>\\n </mrow>\\n \\n <mo>≔</mo>\\n \\n <msub>\\n <mo>∑</mo>\\n \\n <mrow>\\n <mi>i</mi>\\n \\n <mo>⩾</mo>\\n \\n <mn>0</mn>\\n </mrow>\\n </msub>\\n \\n <msub>\\n <mi>a</mi>\\n \\n <mi>i</mi>\\n </msub>\\n \\n <mrow>\\n <mo>(</mo>\\n \\n <mi>G</mi>\\n \\n <mo>)</mo>\\n </mrow>\\n \\n <msup>\\n <mi>x</mi>\\n \\n <mi>i</mi>\\n </msup>\\n </mrow></math>, where <span></span><math>\\n \\n <mrow>\\n <msub>\\n <mi>a</mi>\\n \\n <mi>i</mi>\\n </msub>\\n \\n <mrow>\\n <mo>(</mo>\\n \\n <mi>G</mi>\\n \\n <mo>)</mo>\\n </mrow>\\n </mrow></math> (<span></span><math>\\n \\n <mrow>\\n <mi>i</mi>\\n \\n <mo>⩾</mo>\\n \\n <mn>1</mn>\\n </mrow></math>) is the number of <span></span><math>\\n \\n <mrow>\\n <mi>i</mi>\\n </mrow></math>-cliques in <span></span><math>\\n \\n <mrow>\\n <mi>G</mi>\\n </mrow></math> and <span></span><math>\\n \\n <mrow>\\n <msub>\\n <mi>a</mi>\\n \\n <mn>0</mn>\\n </msub>\\n \\n <mrow>\\n <mo>(</mo>\\n \\n <mi>G</mi>\\n \\n <mo>)</mo>\\n </mrow>\\n \\n <mo>=</mo>\\n \\n <mn>1</mn>\\n </mrow></math>. Equivalently, <span></span><math>\\n \\n <mrow>\\n <mi>C</mi>\\n \\n <mi>l</mi>\\n \\n <mrow>\\n <mo>(</mo>\\n \\n <mrow>\\n <mi>G</mi>\\n \\n <mo>,</mo>\\n \\n <mi>x</mi>\\n </mrow>\\n \\n <mo>)</mo>\\n </mrow>\\n </mrow></math> is exactly the independence polynomial of the complement <span></span><math>\\n \\n <mrow>\\n <mover>\\n <mi>G</mi>\\n \\n <mo>¯</mo>\\n </mover>\\n </mrow></math> of <span></span><math>\\n \\n <mrow>\\n <mi>G</mi>\\n </mrow></math>. The <i>crossing graph</i> <span></span><math>\\n \\n <mrow>\\n <msup>\\n <mi>G</mi>\\n \\n <mi>#</mi>\\n </msup>\\n </mrow></math> of a partial cube <span></span><math>\\n \\n <mrow>\\n <mi>G</mi>\\n </mrow></math> is the graph whose vertices are corresponding to the <span></span><math>\\n \\n <mrow>\\n <mi>Θ</mi>\\n </mrow></math>-classes of <span></span><math>\\n \\n <mrow>\\n <mi>G</mi>\\n </mrow></math>, and two <span></span><math>\\n \\n <mrow>\\n <mi>Θ</mi>\\n </mrow></math>-classes are adjacent in <span></span><math>\\n \\n <mrow>\\n <msup>\\n <mi>G</mi>\\n \\n <mi>#</mi>\\n </msup>\\n </mrow></math> if and only if they cross in <span></span><math>\\n \\n <mrow>\\n <mi>G</mi>\\n </mrow></math>. In the present paper, we prove that for a partial cube <span></span><math>\\n \\n <mrow>\\n <mi>G</mi>\\n </mrow></math>, <span></span><math>\\n \\n <mrow>\\n <mi>C</mi>\\n \\n <mrow>\\n <mo>(</mo>\\n \\n <mrow>\\n <mi>G</mi>\\n \\n <mo>,</mo>\\n \\n <mi>x</mi>\\n </mrow>\\n \\n <mo>)</mo>\\n </mrow>\\n \\n <mo>⩽</mo>\\n \\n <mi>C</mi>\\n \\n <mi>l</mi>\\n \\n <mrow>\\n <mo>(</mo>\\n \\n <mrow>\\n <msup>\\n <mi>G</mi>\\n \\n <mi>#</mi>\\n </msup>\\n \\n <mo>,</mo>\\n \\n <mi>x</mi>\\n \\n <mo>+</mo>\\n \\n <mn>1</mn>\\n </mrow>\\n \\n <mo>)</mo>\\n </mrow>\\n </mrow></math> and the equality holds if and only if <span></span><math>\\n \\n <mrow>\\n <mi>G</mi>\\n </mrow></math> is a median graph. Since every graph can be represented as the crossing graph of a median graph, the above necessary-and-sufficient result shows that the study on the cube polynomials of median graphs can be transformed to the one on the clique polynomials of general graphs (equivalently, on the independence polynomials of their complements). In addition, we disprove the conjecture that the cube polynomials of median graphs are unimodal.</p>\",\"PeriodicalId\":16014,\"journal\":{\"name\":\"Journal of Graph Theory\",\"volume\":\"106 4\",\"pages\":\"907-922\"},\"PeriodicalIF\":0.9000,\"publicationDate\":\"2024-04-23\",\"publicationTypes\":\"Journal Article\",\"fieldsOfStudy\":null,\"isOpenAccess\":false,\"openAccessPdf\":\"\",\"citationCount\":\"0\",\"resultStr\":null,\"platform\":\"Semanticscholar\",\"paperid\":null,\"PeriodicalName\":\"Journal of Graph Theory\",\"FirstCategoryId\":\"100\",\"ListUrlMain\":\"https://onlinelibrary.wiley.com/doi/10.1002/jgt.23099\",\"RegionNum\":3,\"RegionCategory\":\"数学\",\"ArticlePicture\":[],\"TitleCN\":null,\"AbstractTextCN\":null,\"PMCID\":null,\"EPubDate\":\"\",\"PubModel\":\"\",\"JCR\":\"Q2\",\"JCRName\":\"MATHEMATICS\",\"Score\":null,\"Total\":0}","platform":"Semanticscholar","paperid":null,"PeriodicalName":"Journal of Graph Theory","FirstCategoryId":"100","ListUrlMain":"https://onlinelibrary.wiley.com/doi/10.1002/jgt.23099","RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q2","JCRName":"MATHEMATICS","Score":null,"Total":0}
引用次数: 0

摘要

局部立方体是指可以嵌入超立方体的图形。图的立方多项式是Ⅳ的诱导超立方的计数多项式,定义为Ⅳ,其中Ⅳ是Ⅳ的诱导-立方(维数为Ⅳ的超立方)的个数。 Ⅳ的簇多项式定义为Ⅳ,其中()是Ⅳ中簇的个数。等价地,恰好是 的补集的独立性多项式。 部分立方体的交叉图是其顶点对应于 的-类的图,并且当且仅当两个-类在 中交叉时,它们在 中相邻。 在本文中,我们证明对于部分立方体 ,并且当且仅当 是一个中值图时,等价成立。由于每个图都可以表示为中值图的交叉图,上述必要且充分的结果表明,对中值图的立方多项式的研究可以转化为对一般图的簇多项式的研究(等同于对其补集的独立性多项式的研究)。此外,我们还推翻了中值图的立方多项式是单模态的猜想。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
A relation between the cube polynomials of partial cubes and the clique polynomials of their crossing graphs

Partial cubes are the graphs which can be embedded into hypercubes. The cube polynomial of a graph G is a counting polynomial of induced hypercubes of G , which is defined as C ( G , x ) i 0 α i ( G ) x i , where α i ( G ) is the number of induced i -cubes (hypercubes of dimension i ) of G . The clique polynomial of G is defined as C l ( G , x ) i 0 a i ( G ) x i , where a i ( G ) ( i 1 ) is the number of i -cliques in G and a 0 ( G ) = 1 . Equivalently, C l ( G , x ) is exactly the independence polynomial of the complement G ¯ of G . The crossing graph G # of a partial cube G is the graph whose vertices are corresponding to the Θ -classes of G , and two Θ -classes are adjacent in G # if and only if they cross in G . In the present paper, we prove that for a partial cube G , C ( G , x ) C l ( G # , x + 1 ) and the equality holds if and only if G is a median graph. Since every graph can be represented as the crossing graph of a median graph, the above necessary-and-sufficient result shows that the study on the cube polynomials of median graphs can be transformed to the one on the clique polynomials of general graphs (equivalently, on the independence polynomials of their complements). In addition, we disprove the conjecture that the cube polynomials of median graphs are unimodal.

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来源期刊
Journal of Graph Theory
Journal of Graph Theory 数学-数学
CiteScore
1.60
自引率
22.20%
发文量
130
审稿时长
6-12 weeks
期刊介绍: The Journal of Graph Theory is devoted to a variety of topics in graph theory, such as structural results about graphs, graph algorithms with theoretical emphasis, and discrete optimization on graphs. The scope of the journal also includes related areas in combinatorics and the interaction of graph theory with other mathematical sciences. A subscription to the Journal of Graph Theory includes a subscription to the Journal of Combinatorial Designs .
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