Journal of Graph Theory最新文献_第7页

Sharp threshold for embedding balanced spanning trees in random geometric graphs 在随机几何图中嵌入平衡生成树的锐阈值

IF 0.9 3区数学

Journal of Graph Theory Pub Date : 2024-05-09 DOI: 10.1002/jgt.23106

Alberto Espuny Díaz, Lyuben Lichev, Dieter Mitsche, Alexandra Wesolek

{"title":"Sharp threshold for embedding balanced spanning trees in random geometric graphs","authors":"Alberto Espuny Díaz, Lyuben Lichev, Dieter Mitsche, Alexandra Wesolek","doi":"10.1002/jgt.23106","DOIUrl":"10.1002/jgt.23106","url":null,"abstract":"A rooted tree is balanced if the degree of a vertex depends only on its distance to the root. In this paper we determine the sharp threshold for the appearance of a large family of balanced spanning trees in the random geometric graph <math>\u0000 <semantics>\u0000 <mrow>\u0000 <mi>G</mi>\u0000 <mrow>\u0000 <mo>(</mo>\u0000 <mrow>\u0000 <mi>n</mi>\u0000 <mo>,</mo>\u0000 <mi>r</mi>\u0000 <mo>,</mo>\u0000 <mi>d</mi>\u0000 </mrow>\u0000 <mo>)</mo>\u0000 </mrow>\u0000 </mrow>\u0000 <annotation> ${mathscr{G}}(n,r,d)$</annotation>\u0000 </semantics></math>. In particular, we find the sharp threshold for balanced binary trees. More generally, we show that all sequences of balanced trees with uniformly bounded degrees and height tending to infinity appear above a sharp threshold, and none of these appears below the same value. Our results hold more generally for geometric graphs satisfying a mild condition on the distribution of their vertex set, and we provide a polynomial time algorithm to find such trees.","PeriodicalId":16014,"journal":{"name":"Journal of Graph Theory","volume":"107 1","pages":"107-125"},"PeriodicalIF":0.9,"publicationDate":"2024-05-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140933029","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Local degree conditions for K 9 ${K}_{9}$ -minors in graphs 图中 K9 ${K}_{9}$ 未成数的局部度条件

IF 0.9 3区数学

Journal of Graph Theory Pub Date : 2024-05-08 DOI: 10.1002/jgt.23110

Takashige Akiyama

{"title":"Local degree conditions for \u0000 \u0000 \u0000 \u0000 K\u0000 9\u0000 \u0000 \u0000 ${K}_{9}$\u0000 -minors in graphs","authors":"Takashige Akiyama","doi":"10.1002/jgt.23110","DOIUrl":"10.1002/jgt.23110","url":null,"abstract":"We prove that if each edge of a graph <math>\u0000 <semantics>\u0000 <mrow>\u0000 <mi>G</mi>\u0000 </mrow>\u0000 <annotation> $G$</annotation>\u0000 </semantics></math> belongs to at least seven triangles, then <math>\u0000 <semantics>\u0000 <mrow>\u0000 <mi>G</mi>\u0000 </mrow>\u0000 <annotation> $G$</annotation>\u0000 </semantics></math> contains a <math>\u0000 <semantics>\u0000 <mrow>\u0000 <msub>\u0000 <mi>K</mi>\u0000 \u0000 <mn>9</mn>\u0000 </msub>\u0000 </mrow>\u0000 <annotation> ${K}_{9}$</annotation>\u0000 </semantics></math>-minor or contains <math>\u0000 <semantics>\u0000 <mrow>\u0000 <msub>\u0000 <mi>K</mi>\u0000 <mrow>\u0000 <mn>1</mn>\u0000 \u0000 <mo>,</mo>\u0000 \u0000 <mn>2</mn>\u0000 \u0000 <mo>,</mo>\u0000 \u0000 <mn>2</mn>\u0000 \u0000 <mo>,</mo>\u0000 \u0000 <mn>2</mn>\u0000 \u0000 <mo>,</mo>\u0000 \u0000 <mn>2</mn>\u0000 \u0000 <mo>,</mo>\u0000 \u0000 <mn>2</mn>\u0000 </mrow>\u0000 </msub>\u0000 </mrow>\u0000 <annotation> ${K}_{1,2,2,2,2,2}$</annotation>\u0000 </semantics></math> as an induced subgraph. This result was conjectured by Albar and Gonçalves in 2018. Moreover, we apply this result to study the stress freeness of graphs.","PeriodicalId":16014,"journal":{"name":"Journal of Graph Theory","volume":"107 1","pages":"70-94"},"PeriodicalIF":0.9,"publicationDate":"2024-05-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140933027","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Spanning even trees of graphs 图的跨偶数树

IF 0.9 3区数学

Journal of Graph Theory Pub Date : 2024-05-08 DOI: 10.1002/jgt.23115

Bill Jackson, Kiyoshi Yoshimoto

{"title":"Spanning even trees of graphs","authors":"Bill Jackson, Kiyoshi Yoshimoto","doi":"10.1002/jgt.23115","DOIUrl":"10.1002/jgt.23115","url":null,"abstract":"A tree <math>\u0000 <semantics>\u0000 <mrow>\u0000 <mi>T</mi>\u0000 </mrow>\u0000 <annotation> $T$</annotation>\u0000 </semantics></math> is said to be even if all pairs of vertices of degree one in <math>\u0000 <semantics>\u0000 <mrow>\u0000 <mi>T</mi>\u0000 </mrow>\u0000 <annotation> $T$</annotation>\u0000 </semantics></math> are joined by a path of even length. We conjecture that every <math>\u0000 <semantics>\u0000 <mrow>\u0000 <mi>r</mi>\u0000 </mrow>\u0000 <annotation> $r$</annotation>\u0000 </semantics></math>-regular nonbipartite connected graph <math>\u0000 <semantics>\u0000 <mrow>\u0000 <mi>G</mi>\u0000 </mrow>\u0000 <annotation> $G$</annotation>\u0000 </semantics></math> has a spanning even tree and verify this conjecture when <math>\u0000 <semantics>\u0000 <mrow>\u0000 <mi>G</mi>\u0000 </mrow>\u0000 <annotation> $G$</annotation>\u0000 </semantics></math> has a 2-factor. Well-known results of Petersen and Hanson et al. imply that the only remaining unsolved case is when <math>\u0000 <semantics>\u0000 <mrow>\u0000 <mi>r</mi>\u0000 </mrow>\u0000 <annotation> $r$</annotation>\u0000 </semantics></math> is odd and <math>\u0000 <semantics>\u0000 <mrow>\u0000 <mi>G</mi>\u0000 </mrow>\u0000 <annotation> $G$</annotation>\u0000 </semantics></math> has at least <math>\u0000 <semantics>\u0000 <mrow>\u0000 <mi>r</mi>\u0000 </mrow>\u0000 <annotation> $r$</annotation>\u0000 </semantics></math> bridges. We investigate this case further and propose some related conjectures.","PeriodicalId":16014,"journal":{"name":"Journal of Graph Theory","volume":"107 1","pages":"95-106"},"PeriodicalIF":0.9,"publicationDate":"2024-05-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140933030","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Graphs with at most two moplexes 最多有两个横线的图形

IF 0.9 3区数学

Journal of Graph Theory Pub Date : 2024-05-08 DOI: 10.1002/jgt.23102

Clément Dallard, Robert Ganian, Meike Hatzel, Matjaž Krnc, Martin Milanič

{"title":"Graphs with at most two moplexes","authors":"Clément Dallard, Robert Ganian, Meike Hatzel, Matjaž Krnc, Martin Milanič","doi":"10.1002/jgt.23102","DOIUrl":"10.1002/jgt.23102","url":null,"abstract":"A moplex is a natural graph structure that arises when lifting Dirac's classical theorem from chordal graphs to general graphs. The notion is known to be closely related to lexicographic searches in graphs as well as to asteroidal triples, and has been applied in several algorithms related to graph classes, such as interval graphs, claw-free, and diamond-free graphs. However, while every noncomplete graph has at least two moplexes, little is known about structural properties of graphs with a bounded number of moplexes. The study of these graphs is, in part, motivated by the parallel between moplexes in general graphs and simplicial modules in chordal graphs: unlike in the moplex setting, properties of chordal graphs with a bounded number of simplicial modules are well understood. For instance, chordal graphs having at most two simplicial modules are intervals. In this work, we initiate an investigation of <math>\u0000 <semantics>\u0000 <mrow>\u0000 <mi>k</mi>\u0000 </mrow>\u0000 <annotation> $k$</annotation>\u0000 </semantics></math>-moplex graphs, which are defined as graphs containing at most <math>\u0000 <semantics>\u0000 <mrow>\u0000 <mi>k</mi>\u0000 </mrow>\u0000 <annotation> $k$</annotation>\u0000 </semantics></math> moplexes. Of particular interest is the smallest nontrivial case <math>\u0000 <semantics>\u0000 <mrow>\u0000 <mi>k</mi>\u0000 \u0000 <mo>=</mo>\u0000 \u0000 <mn>2</mn>\u0000 </mrow>\u0000 <annotation> $k=2$</annotation>\u0000 </semantics></math>, which forms a counterpart to the class of interval graphs. As our main structural result, we show that, when restricted to connected graphs, the class of 2-moplex graphs is sandwiched between the classes of proper interval graphs and cocomparability graphs; moreover, both inclusions are tight for hereditary classes. From a complexity-theoretic viewpoint, this leads to the natural question of whether the presence of at most two moplexes guarantees a sufficient amount of structure to efficiently solve problems that are known to be intractable on cocomparability graphs, but not on proper interval graphs. We develop new reductions that answer this question negatively for two prominent problems fitting this profile, namely, \u0000Graph Isomorphism and \u0000Max-Cut. On the other hand, we prove that every connected 2-moplex graph contains a Hamiltonian path, generalising the same property of connected proper interval graphs. Furthermore, for graphs with a higher number of moplexes, we lift the previously known result that graphs without asteroidal triples have at most two moplexes to the more general setting of larger asteroidal sets.","PeriodicalId":16014,"journal":{"name":"Journal of Graph Theory","volume":"107 1","pages":"38-69"},"PeriodicalIF":0.9,"publicationDate":"2024-05-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1002/jgt.23102","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140933032","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Gallai-like characterization of strong cocomparability graphs 强可比性图的伽来样表征

IF 0.9 3区数学

Journal of Graph Theory Pub Date : 2024-05-06 DOI: 10.1002/jgt.23113

Jing Huang

{"title":"Gallai-like characterization of strong cocomparability graphs","authors":"Jing Huang","doi":"10.1002/jgt.23113","DOIUrl":"10.1002/jgt.23113","url":null,"abstract":"Strong cocomparability graphs are the reflexive graphs whose adjacency matrix can be rearranged by a simultaneous row and column permutation to avoid the submatrix with rows <math>\u0000 <semantics>\u0000 <mrow>\u0000 <mn>01</mn>\u0000 \u0000 <mo>,</mo>\u0000 \u0000 <mn>10</mn>\u0000 </mrow>\u0000 <annotation> $01,10$</annotation>\u0000 </semantics></math>. Strong cocomparability graphs form a subclass of cocomparability graphs (i.e., the complements of comparability graphs) and can be recognized in polynomial time. In his seminal paper, Gallai characterized cocomparability graphs in terms of a forbidden structure called asteroids. Gallai proved that cocomparability graphs are precisely those reflexive graphs which do not contain asteroids. In this paper, we give a characterization of strong cocomparability graphs which is analogous to Gallai's characterization for cocomparability graphs. We prove that strong cocomparability graphs are precisely those reflexive graphs which do not contain weak edge-asteroids (a weaker version of asteroids). Our characterization also leads to a polynomial time recognition algorithm for strong cocomparability graphs.","PeriodicalId":16014,"journal":{"name":"Journal of Graph Theory","volume":"107 1","pages":"29-37"},"PeriodicalIF":0.9,"publicationDate":"2024-05-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140933025","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

On the number of minimum dominating sets and total dominating sets in forests 论森林中最小支配集和总支配集的数量

IF 0.9 3区数学

Journal of Graph Theory Pub Date : 2024-04-29 DOI: 10.1002/jgt.23107

Jan Petr, Julien Portier, Leo Versteegen

{"title":"On the number of minimum dominating sets and total dominating sets in forests","authors":"Jan Petr, Julien Portier, Leo Versteegen","doi":"10.1002/jgt.23107","DOIUrl":"10.1002/jgt.23107","url":null,"abstract":"We show that the maximum number of minimum dominating sets of a forest with domination number <math>\u0000 \u0000 <mrow>\u0000 <mi>γ</mi>\u0000 </mrow></math> is at most <math>\u0000 \u0000 <mrow>\u0000 <msup>\u0000 <msqrt>\u0000 <mn>5</mn>\u0000 </msqrt>\u0000 \u0000 <mi>γ</mi>\u0000 </msup>\u0000 </mrow></math> and construct for each <math>\u0000 \u0000 <mrow>\u0000 <mi>γ</mi>\u0000 </mrow></math> a tree with domination number <math>\u0000 \u0000 <mrow>\u0000 <mi>γ</mi>\u0000 </mrow></math> that has more than <math>\u0000 \u0000 <mrow>\u0000 <mfrac>\u0000 <mn>2</mn>\u0000 \u0000 <mn>5</mn>\u0000 </mfrac>\u0000 \u0000 <msup>\u0000 <msqrt>\u0000 <mn>5</mn>\u0000 </msqrt>\u0000 \u0000 <mi>γ</mi>\u0000 </msup>\u0000 </mrow></math> minimum dominating sets. Furthermore, we disprove a conjecture about the number of minimum total dominating sets in forests by Henning, Mohr and Rautenbach.","PeriodicalId":16014,"journal":{"name":"Journal of Graph Theory","volume":"106 4","pages":"976-993"},"PeriodicalIF":0.9,"publicationDate":"2024-04-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1002/jgt.23107","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140833312","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

On λ $lambda $ -backbone coloring of cliques with tree backbones in linear time 在线性时间内对具有树状骨干的小群进行λ $lambda $骨干着色

IF 0.9 3区数学

Journal of Graph Theory Pub Date : 2024-04-29 DOI: 10.1002/jgt.23108

Krzysztof Michalik, Krzysztof Turowski

{"title":"On \u0000 \u0000 \u0000 λ\u0000 \u0000 $lambda $\u0000 -backbone coloring of cliques with tree backbones in linear time","authors":"Krzysztof Michalik, Krzysztof Turowski","doi":"10.1002/jgt.23108","DOIUrl":"10.1002/jgt.23108","url":null,"abstract":"A <math>\u0000 <semantics>\u0000 <mrow>\u0000 <mi>λ</mi>\u0000 </mrow>\u0000 <annotation> $lambda $</annotation>\u0000 </semantics></math>-backbone coloring of a graph <math>\u0000 <semantics>\u0000 <mrow>\u0000 <mi>G</mi>\u0000 </mrow>\u0000 <annotation> $G$</annotation>\u0000 </semantics></math> with its subgraph (also called a backbone) <math>\u0000 <semantics>\u0000 <mrow>\u0000 <mi>H</mi>\u0000 </mrow>\u0000 <annotation> $H$</annotation>\u0000 </semantics></math> is a function <math>\u0000 <semantics>\u0000 <mrow>\u0000 <mi>c</mi>\u0000 \u0000 <mo>:</mo>\u0000 \u0000 <mi>V</mi>\u0000 <mrow>\u0000 <mo>(</mo>\u0000 \u0000 <mi>G</mi>\u0000 \u0000 <mo>)</mo>\u0000 </mrow>\u0000 \u0000 <mo>→</mo>\u0000 <mrow>\u0000 <mo>{</mo>\u0000 <mrow>\u0000 <mn>1</mn>\u0000 \u0000 <mo>,</mo>\u0000 \u0000 <mi>…</mi>\u0000 \u0000 <mo>,</mo>\u0000 \u0000 <mi>k</mi>\u0000 </mrow>\u0000 \u0000 <mo>}</mo>\u0000 </mrow>\u0000 </mrow>\u0000 <annotation> $c:V(G)to {1,ldots ,k}$</annotation>\u0000 </semantics></math> ensuring that <math>\u0000 <semantics>\u0000 <mrow>\u0000 <mi>c</mi>\u0000 </mrow>\u0000 <annotation> $c$</annotation>\u0000 </semantics></math> is a proper coloring of <math>\u0000 <semantics>\u0000 <mrow>\u0000 <mi>G</mi>\u0000 </mrow>\u0000 <annotation> $G$</annotation>\u0000 </semantics></math> and for each <math>\u0000 <semantics>\u0000 <mrow>\u0000 <mrow>\u0000 <mo>{</mo>\u0000 <mrow>\u0000 <mi>u</mi>\u0000 \u0000 <mo>,</mo>\u0000 \u0000 <mi>v</mi>\u0000 </mrow>\u0000 \u0000 <mo>}</mo>\u0000 </mrow>\u0000 \u0000 <mo>∈</mo>\u0000 \u0000 <mi>E</mi>\u0000 <mrow>\u0000 <mo>(</mo>\u0000 \u0000 <mi>H</mi>\u0000 \u0000 <mo>)</mo>\u0000 </mrow>\u0000 </mrow>\u0000 <annotation> ${u,v}in E(H)$</annotation>\u0000 </semantics></math> it holds that <math>\u0000 ","PeriodicalId":16014,"journal":{"name":"Journal of Graph Theory","volume":"107 1","pages":"5-28"},"PeriodicalIF":0.9,"publicationDate":"2024-04-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140833219","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Cycle-factors in oriented graphs 定向图中的循环因子

IF 0.9 3区数学

Journal of Graph Theory Pub Date : 2024-04-25 DOI: 10.1002/jgt.23105

Zhilan Wang, Jin Yan, Jie Zhang

{"title":"Cycle-factors in oriented graphs","authors":"Zhilan Wang, Jin Yan, Jie Zhang","doi":"10.1002/jgt.23105","DOIUrl":"10.1002/jgt.23105","url":null,"abstract":"Let <math>\u0000 \u0000 <mrow>\u0000 <mi>k</mi>\u0000 </mrow></math> be a positive integer. A <math>\u0000 \u0000 <mrow>\u0000 <mi>k</mi>\u0000 </mrow></math>-cycle-factor of an oriented graph is a set of disjoint cycles of length <math>\u0000 \u0000 <mrow>\u0000 <mi>k</mi>\u0000 </mrow></math> that covers all vertices of the graph. In this paper, we prove that there exists a positive constant <math>\u0000 \u0000 <mrow>\u0000 <mi>c</mi>\u0000 </mrow></math> such that for <math>\u0000 \u0000 <mrow>\u0000 <mi>n</mi>\u0000 </mrow></math> sufficiently large, any oriented graph on <math>\u0000 \u0000 <mrow>\u0000 <mi>n</mi>\u0000 </mrow></math> vertices with both minimum out-degree and minimum in-degree at least <math>\u0000 \u0000 <mrow>\u0000 <mrow>\u0000 <mo>(</mo>\u0000 \u0000 <mrow>\u0000 <mn>1</mn>\u0000 \u0000 <mo>∕</mo>\u0000 \u0000 <mn>2</mn>\u0000 \u0000 <mo>−</mo>\u0000 \u0000 <mi>c</mi>\u0000 </mrow>\u0000 \u0000 <mo>)</mo>\u0000 </mrow>\u0000 \u0000 <mi>n</mi>\u0000 </mrow></math> contains a <math>\u0000 \u0000 <mrow>\u0000 <mi>k</mi>\u0000 </mrow></math>-cycle-factor for any <math>\u0000 \u0000 <mrow>\u0000 <mi>k</mi>\u0000 \u0000 <mo>≥</mo>\u0000 \u0000 <mn>4</mn>\u0000 </mrow></math>. Additionally, under the same hypotheses, we also show that for any sequence <math>\u0000 \u0000 <mrow>\u0000 <msub>\u0000 <mi>n</mi>\u0000 \u0000 <mn>1</mn>\u0000 </msub>\u0000 \u0000 <mo>,</mo>\u0000 \u0000 <mo>…</mo>\u0000 \u0000 <mo>,</mo>\u0000 \u0000 <msub>\u0000 <mi>n</mi>\u0000 \u0000 <mi>t</mi>\u0000 </msub>\u0000 </mrow></math> with <math>\u0000 \u0000 <mrow>\u0000 <msubsup>\u0000 <mo>∑</mo>\u0000 \u0000 <mrow>\u0000 <mi>i</mi>\u0000 \u0000 <mo>=</mo>\u0000 \u0000 <mn>1</mn>\u0000 </mrow>\u0000 \u0000 <mi>t</mi>\u0000 </msubsup>\u0000 \u0000 <msub>\u0000 <mi>n</mi>\u0000 \u0000 <mi>i</mi>\u0000 </msub>\u0000 \u0000 <mo>=</mo>\u0000 \u0000 <mi>n","PeriodicalId":16014,"journal":{"name":"Journal of Graph Theory","volume":"106 4","pages":"947-975"},"PeriodicalIF":0.9,"publicationDate":"2024-04-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140803751","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Another proof of Seymour's 6-flow theorem 西摩 6 流定理的另一个证明

IF 0.9 3区数学

Journal of Graph Theory Pub Date : 2024-04-25 DOI: 10.1002/jgt.23091

Matt DeVos, Jessica McDonald, Kathryn Nurse

{"title":"Another proof of Seymour's 6-flow theorem","authors":"Matt DeVos, Jessica McDonald, Kathryn Nurse","doi":"10.1002/jgt.23091","DOIUrl":"10.1002/jgt.23091","url":null,"abstract":"In 1981 Seymour proved his famous 6-flow theorem asserting that every 2-edge-connected graph has a nowhere-zero flow in the group <math>\u0000 \u0000 <mrow>\u0000 <msub>\u0000 <mi>Z</mi>\u0000 \u0000 <mn>2</mn>\u0000 </msub>\u0000 \u0000 <mo>×</mo>\u0000 \u0000 <msub>\u0000 <mi>Z</mi>\u0000 \u0000 <mn>3</mn>\u0000 </msub>\u0000 </mrow></math> (in fact, he offers two proofs of this result). In this note, we give a new short proof of a generalization of this theorem where <math>\u0000 \u0000 <mrow>\u0000 <msub>\u0000 <mi>Z</mi>\u0000 \u0000 <mn>2</mn>\u0000 </msub>\u0000 \u0000 <mo>×</mo>\u0000 \u0000 <msub>\u0000 <mi>Z</mi>\u0000 \u0000 <mn>3</mn>\u0000 </msub>\u0000 </mrow></math>-valued functions are found subject to certain boundary constraints.","PeriodicalId":16014,"journal":{"name":"Journal of Graph Theory","volume":"106 4","pages":"944-946"},"PeriodicalIF":0.9,"publicationDate":"2024-04-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1002/jgt.23091","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140803984","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Tree independence number I. (Even hole, diamond, pyramid)-free graphs 树独立性编号 I. 无（偶数孔、菱形、金字塔）图形

IF 0.9 3区数学

Journal of Graph Theory Pub Date : 2024-04-24 DOI: 10.1002/jgt.23104

Tara Abrishami, Bogdan Alecu, Maria Chudnovsky, Sepehr Hajebi, Sophie Spirkl, Kristina Vušković

{"title":"Tree independence number I. (Even hole, diamond, pyramid)-free graphs","authors":"Tara Abrishami, Bogdan Alecu, Maria Chudnovsky, Sepehr Hajebi, Sophie Spirkl, Kristina Vušković","doi":"10.1002/jgt.23104","DOIUrl":"10.1002/jgt.23104","url":null,"abstract":"The tree-independence number <math>\u0000 \u0000 <mrow>\u0000 <mstyle>\u0000 <mtext>tree-</mtext>\u0000 </mstyle>\u0000 \u0000 <mi>α</mi>\u0000 </mrow></math>, first defined and studied by Dallard, Milanič, and Štorgel, is a variant of treewidth tailored to solving the maximum independent set problem. Over a series of papers, Abrishami et al. developed the so-called central bag method to study induced obstructions to bounded treewidth. Among others, they showed that, in a certain superclass <math>\u0000 \u0000 <mrow>\u0000 <mi>C</mi>\u0000 </mrow></math> of (even hole, diamond, pyramid)-free graphs, treewidth is bounded by a function of the clique number. In this paper, we relax the bounded clique number assumption, and show that <math>\u0000 \u0000 <mrow>\u0000 <mi>C</mi>\u0000 </mrow></math> has bounded <math>\u0000 \u0000 <mrow>\u0000 <mstyle>\u0000 <mspace></mspace>\u0000 \u0000 <mtext>tree-</mtext>\u0000 <mspace></mspace>\u0000 </mstyle>\u0000 \u0000 <mi>α</mi>\u0000 </mrow></math>. Via existing results, this yields a polynomial-time algorithm for the Maximum Weight Independent Set problem in this class. Our result also corroborates, for this class of graphs, a conjecture of Dallard, Milanič, and Štorgel that in a hereditary graph class, <math>\u0000 \u0000 <mrow>\u0000 <mstyle>\u0000 <mspace></mspace>\u0000 \u0000 <mtext>tree-</mtext>\u0000 <mspace></mspace>\u0000 </mstyle>\u0000 \u0000 <mi>α</mi>\u0000 </mrow></math> is bounded if and only if the treewidth is bounded by a function of the clique number.","PeriodicalId":16014,"journal":{"name":"Journal of Graph Theory","volume":"106 4","pages":"923-943"},"PeriodicalIF":0.9,"publicationDate":"2024-04-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1002/jgt.23104","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140661033","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

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