Pub Date : 2025-12-08DOI: 10.1016/j.disc.2025.114914
Ruike Wang, Zhenzhen Lou
Spectral stability theorems have been a crucial aspect of graph theory research. Consider a graph G with size m and spectral radius . Building on the solid foundation laid by previous works in this rich field, this paper presents novel and valuable findings related to stability. Wang and Guo (2024) [16] showed an important result. Given that and , when , then G contains either a quadrilateral or a star of size . In this paper, we take a significant step forward by generalizing this result. Precisely, for and , when , we prove that G contains either a copy of (a complete bipartite graph with two vertices on one side and t vertices on the other side) or a star of size . This generalization contributes to a more profound understanding of the spectral and structural aspects of graphs, as well as their stability properties.
谱稳定性定理一直是图论研究的一个重要方面。考虑一个大小为m,谱半径为ρ(G)的图G。本文在前人在这一丰富领域的工作奠定的坚实基础上,提出了与稳定性有关的新颖而有价值的发现。Wang and Guo(2024)[16]给出了重要的结果。设m=Ω(k4)且k≥0,当ρ(G)≥m - k时,则G包含大小为m - k的四边形或星形。在本文中,我们通过推广这一结果向前迈出了重要的一步。准确地说,对于m=Ω(k4)和2≤t≤k+2,当ρ(G)≥m−k+t−2时,我们证明了G包含K2的一个副本,t(一侧有两个顶点,另一侧有t个顶点的完全二部图)或一个大小为m−k+t−2的星。这种推广有助于更深刻地理解图的谱和结构方面,以及它们的稳定性。
{"title":"A spectral stability result regarding the complete bipartite graph K2,t","authors":"Ruike Wang, Zhenzhen Lou","doi":"10.1016/j.disc.2025.114914","DOIUrl":"10.1016/j.disc.2025.114914","url":null,"abstract":"<div><div>Spectral stability theorems have been a crucial aspect of graph theory research. Consider a graph <em>G</em> with size <em>m</em> and spectral radius <span><math><mi>ρ</mi><mo>(</mo><mi>G</mi><mo>)</mo></math></span>. Building on the solid foundation laid by previous works in this rich field, this paper presents novel and valuable findings related to stability. Wang and Guo (2024) <span><span>[16]</span></span> showed an important result. Given that <span><math><mi>m</mi><mo>=</mo><mi>Ω</mi><mo>(</mo><msup><mrow><mi>k</mi></mrow><mrow><mn>4</mn></mrow></msup><mo>)</mo></math></span> and <span><math><mi>k</mi><mo>≥</mo><mn>0</mn></math></span>, when <span><math><mi>ρ</mi><mo>(</mo><mi>G</mi><mo>)</mo><mo>≥</mo><msqrt><mrow><mi>m</mi><mo>−</mo><mi>k</mi></mrow></msqrt></math></span>, then <em>G</em> contains either a quadrilateral or a star of size <span><math><mi>m</mi><mo>−</mo><mi>k</mi></math></span>. In this paper, we take a significant step forward by generalizing this result. Precisely, for <span><math><mi>m</mi><mo>=</mo><mi>Ω</mi><mo>(</mo><msup><mrow><mi>k</mi></mrow><mrow><mn>4</mn></mrow></msup><mo>)</mo></math></span> and <span><math><mn>2</mn><mo>≤</mo><mi>t</mi><mo>≤</mo><mi>k</mi><mo>+</mo><mn>2</mn></math></span>, when <span><math><mi>ρ</mi><mo>(</mo><mi>G</mi><mo>)</mo><mo>≥</mo><msqrt><mrow><mi>m</mi><mo>−</mo><mi>k</mi><mo>+</mo><mi>t</mi><mo>−</mo><mn>2</mn></mrow></msqrt></math></span>, we prove that <em>G</em> contains either a copy of <span><math><msub><mrow><mi>K</mi></mrow><mrow><mn>2</mn><mo>,</mo><mi>t</mi></mrow></msub></math></span> (a complete bipartite graph with two vertices on one side and <em>t</em> vertices on the other side) or a star of size <span><math><mi>m</mi><mo>−</mo><mi>k</mi><mo>+</mo><mi>t</mi><mo>−</mo><mn>2</mn></math></span>. This generalization contributes to a more profound understanding of the spectral and structural aspects of graphs, as well as their stability properties.</div></div>","PeriodicalId":50572,"journal":{"name":"Discrete Mathematics","volume":"349 5","pages":"Article 114914"},"PeriodicalIF":0.7,"publicationDate":"2025-12-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145697781","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}
Pub Date : 2025-12-08DOI: 10.1016/j.disc.2025.114915
Hyunsoo Cho , Ho-Hyeong Lee , Kyeongjun Lee , Hayan Nam , Jaebum Sohn
Huang and Wang began counting the number of simultaneous core partitions with the fixed number of corners. They enumerated the number of -core partitions with m corners and -core partitions with m corners. Later, Cho, Huh, and Sohn gave a formula for the number of -core partitions with m corners. In this paper, we show an expression for the number of -core partitions with m corners.
{"title":"Corners of (t,tk ± 1)-core partitions","authors":"Hyunsoo Cho , Ho-Hyeong Lee , Kyeongjun Lee , Hayan Nam , Jaebum Sohn","doi":"10.1016/j.disc.2025.114915","DOIUrl":"10.1016/j.disc.2025.114915","url":null,"abstract":"<div><div>Huang and Wang began counting the number of simultaneous core partitions with the fixed number of corners. They enumerated the number of <span><math><mo>(</mo><mi>t</mi><mo>,</mo><mi>t</mi><mo>+</mo><mn>1</mn><mo>)</mo></math></span>-core partitions with <em>m</em> corners and <span><math><mo>(</mo><mi>t</mi><mo>,</mo><mi>t</mi><mo>+</mo><mn>1</mn><mo>,</mo><mi>t</mi><mo>+</mo><mn>2</mn><mo>)</mo></math></span>-core partitions with <em>m</em> corners. Later, Cho, Huh, and Sohn gave a formula for the number of <span><math><mo>(</mo><mi>t</mi><mo>,</mo><mi>t</mi><mo>+</mo><mn>1</mn><mo>,</mo><mo>…</mo><mo>,</mo><mi>t</mi><mo>+</mo><mi>p</mi><mo>)</mo></math></span>-core partitions with <em>m</em> corners. In this paper, we show an expression for the number of <span><math><mo>(</mo><mi>t</mi><mo>,</mo><mi>t</mi><mi>k</mi><mo>±</mo><mn>1</mn><mo>)</mo></math></span>-core partitions with <em>m</em> corners.</div></div>","PeriodicalId":50572,"journal":{"name":"Discrete Mathematics","volume":"349 5","pages":"Article 114915"},"PeriodicalIF":0.7,"publicationDate":"2025-12-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145697836","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}
Pub Date : 2025-12-08DOI: 10.1016/j.disc.2025.114937
Meng Liu , Yusheng Li
For a graph G, a connected graph H is said to be G-good if the Ramsey number is equal to the lower bound , where and are the chromatic number and the chromatic surplus of G, respectively. Let be the book graph that consists of n copies of sharing a common . Recently, avoiding use of the regularity lemma, Fox, He and Wigderson (2023) revisit several Ramsey goodness results involving books. They commented that it would be very interesting to see how far one can push these ideas. In this paper, we describe graphs G with exactly such that are G-good for large n, where the size of a color class of G can be at most δn for some .
{"title":"Ramsey goodness of large books revisited","authors":"Meng Liu , Yusheng Li","doi":"10.1016/j.disc.2025.114937","DOIUrl":"10.1016/j.disc.2025.114937","url":null,"abstract":"<div><div>For a graph <em>G</em>, a connected graph <em>H</em> is said to be <em>G</em>-good if the Ramsey number <span><math><mi>r</mi><mo>(</mo><mi>G</mi><mo>,</mo><mi>H</mi><mo>)</mo></math></span> is equal to the lower bound <span><math><mo>(</mo><mi>χ</mi><mo>(</mo><mi>G</mi><mo>)</mo><mo>−</mo><mn>1</mn><mo>)</mo><mo>(</mo><mo>|</mo><mi>H</mi><mo>|</mo><mo>−</mo><mn>1</mn><mo>)</mo><mo>+</mo><mi>s</mi><mo>(</mo><mi>G</mi><mo>)</mo></math></span>, where <span><math><mi>χ</mi><mo>(</mo><mi>G</mi><mo>)</mo></math></span> and <span><math><mi>s</mi><mo>(</mo><mi>G</mi><mo>)</mo></math></span> are the chromatic number and the chromatic surplus of <em>G</em>, respectively. Let <span><math><msub><mrow><mi>B</mi></mrow><mrow><mi>k</mi></mrow></msub><mo>(</mo><mi>n</mi><mo>)</mo></math></span> be the book graph that consists of <em>n</em> copies of <span><math><msub><mrow><mi>K</mi></mrow><mrow><mi>k</mi><mo>+</mo><mn>1</mn></mrow></msub></math></span> sharing a common <span><math><msub><mrow><mi>K</mi></mrow><mrow><mi>k</mi></mrow></msub></math></span>. Recently, avoiding use of the regularity lemma, Fox, He and Wigderson (2023) revisit several Ramsey goodness results involving books. They commented that it would be very interesting to see how far one can push these ideas. In this paper, we describe graphs <em>G</em> with <span><math><mi>s</mi><mo>(</mo><mi>G</mi><mo>)</mo><mo>=</mo><mn>1</mn></math></span> exactly such that <span><math><msub><mrow><mi>B</mi></mrow><mrow><mi>k</mi></mrow></msub><mo>(</mo><mi>n</mi><mo>)</mo></math></span> are <em>G</em>-good for large <em>n</em>, where the size of a color class of <em>G</em> can be at most <em>δn</em> for some <span><math><mi>δ</mi><mo>></mo><mn>0</mn></math></span>.</div></div>","PeriodicalId":50572,"journal":{"name":"Discrete Mathematics","volume":"349 5","pages":"Article 114937"},"PeriodicalIF":0.7,"publicationDate":"2025-12-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145697837","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}
Pub Date : 2025-12-08DOI: 10.1016/j.disc.2025.114939
Siyan Liu , Rong-Xia Hao , Rong Luo , Cun-Quan Zhang
A k-bisection (resp. k-quasi-bisection) of a bridgeless cubic graph G is a vertex 2-coloring satisfying: (i) the sizes of the two color classes are equal (resp. the sizes of the two color classes differ by at most 2), and (ii) the order of each connected component induced by each color class is at most k. Esperet et al. (2017) [7] conjectured that any cubic graph admits a 2-quasi-bisection. In this paper, we prove this conjecture for all bridgeless cubic graphs with oddness 2.
k-二分法。无桥三次图G的k-拟对分(k-拟对分)是顶点2着色,满足:(i)两个颜色类的大小相等(相对于;两个颜色类的大小相差不超过2),并且(ii)每个颜色类诱导的每个连通分量的阶数不超过k。Esperet et al.(2017)[7]推测任何三次图都允许2-拟对分。本文对奇异数为2的所有无桥三次图证明了这一猜想。
{"title":"A note on 2-quasi-bisection of cubic graphs with oddness 2","authors":"Siyan Liu , Rong-Xia Hao , Rong Luo , Cun-Quan Zhang","doi":"10.1016/j.disc.2025.114939","DOIUrl":"10.1016/j.disc.2025.114939","url":null,"abstract":"<div><div>A <em>k</em>-bisection (resp. <em>k</em>-quasi-bisection) of a bridgeless cubic graph <em>G</em> is a vertex 2-coloring satisfying: (i) the sizes of the two color classes are equal (resp. the sizes of the two color classes differ by at most 2), and (ii) the order of each connected component induced by each color class is at most <em>k</em>. Esperet et al. (2017) <span><span>[7]</span></span> conjectured that any cubic graph admits a 2-quasi-bisection. In this paper, we prove this conjecture for all bridgeless cubic graphs with oddness 2.</div></div>","PeriodicalId":50572,"journal":{"name":"Discrete Mathematics","volume":"349 5","pages":"Article 114939"},"PeriodicalIF":0.7,"publicationDate":"2025-12-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145697782","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}
Pub Date : 2025-12-08DOI: 10.1016/j.disc.2025.114913
William J. Wesley
We prove new bounds for Ramsey numbers for book graphs . In particular, we show that for an infinite family of n using a block-circulant construction similar to Paley graphs. We obtain improved bounds for several other values of using different block-circulant graphs from SAT and integer programming (IP) solvers. Finally, we enumerate the number of critical graphs for for small r and s using SAT modulo symmetries (SMS).
{"title":"Lower bounds for book Ramsey numbers","authors":"William J. Wesley","doi":"10.1016/j.disc.2025.114913","DOIUrl":"10.1016/j.disc.2025.114913","url":null,"abstract":"<div><div>We prove new bounds for Ramsey numbers for book graphs <span><math><msub><mrow><mi>B</mi></mrow><mrow><mi>n</mi></mrow></msub></math></span>. In particular, we show that <span><math><mi>R</mi><mo>(</mo><msub><mrow><mi>B</mi></mrow><mrow><mi>n</mi><mo>−</mo><mn>1</mn></mrow></msub><mo>,</mo><msub><mrow><mi>B</mi></mrow><mrow><mi>n</mi></mrow></msub><mo>)</mo><mo>=</mo><mn>4</mn><mi>n</mi><mo>−</mo><mn>1</mn></math></span> for an infinite family of <em>n</em> using a block-circulant construction similar to Paley graphs. We obtain improved bounds for several other values of <span><math><mi>R</mi><mo>(</mo><msub><mrow><mi>B</mi></mrow><mrow><mi>r</mi></mrow></msub><mo>,</mo><msub><mrow><mi>B</mi></mrow><mrow><mi>s</mi></mrow></msub><mo>)</mo></math></span> using different block-circulant graphs from SAT and integer programming (IP) solvers. Finally, we enumerate the number of critical graphs for <span><math><mi>R</mi><mo>(</mo><msub><mrow><mi>B</mi></mrow><mrow><mi>r</mi></mrow></msub><mo>,</mo><msub><mrow><mi>B</mi></mrow><mrow><mi>s</mi></mrow></msub><mo>)</mo></math></span> for small <em>r</em> and <em>s</em> using SAT modulo symmetries (SMS).</div></div>","PeriodicalId":50572,"journal":{"name":"Discrete Mathematics","volume":"349 5","pages":"Article 114913"},"PeriodicalIF":0.7,"publicationDate":"2025-12-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145697834","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}
Pub Date : 2025-12-08DOI: 10.1016/j.disc.2025.114916
Wenxia Qu , Wenston J.T. Zang
In this paper, we present the bilateral truncated identity of the quintuple product identity, which is a generalization of the truncated quintuple product identities given by Chan et al. (2016) [6]. Additionally, we provide the bilateral truncated forms of two q-series identities, which are well-known consequences of the quintuple product identity.
{"title":"Bilateral truncated quintuple product identity","authors":"Wenxia Qu , Wenston J.T. Zang","doi":"10.1016/j.disc.2025.114916","DOIUrl":"10.1016/j.disc.2025.114916","url":null,"abstract":"<div><div>In this paper, we present the bilateral truncated identity of the quintuple product identity, which is a generalization of the truncated quintuple product identities given by Chan et al. (2016) <span><span>[6]</span></span>. Additionally, we provide the bilateral truncated forms of two <em>q</em>-series identities, which are well-known consequences of the quintuple product identity.</div></div>","PeriodicalId":50572,"journal":{"name":"Discrete Mathematics","volume":"349 5","pages":"Article 114916"},"PeriodicalIF":0.7,"publicationDate":"2025-12-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145697835","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}
Pub Date : 2025-12-08DOI: 10.1016/j.disc.2025.114935
Yaozong Zhang, Dabin Zheng, Xiaoqiang Wang
Self-orthogonal codes are a subclass of linear codes that are contained within their dual codes. Since self-orthogonal codes are widely used in quantum codes, lattice theory and linear complementary dual (LCD) codes, they have received continuous attention and research. In this paper, we construct a class of self-orthogonal codes by using the defining-set approach, and determine their weight distributions and the parameters of their dual codes. Some considered codes are optimal according to the tables of best codes known maintained at [11] and a class of almost maximum distance separable (AMDS) codes from their duals is obtained. As applications, we obtain a class of new quantum codes, which are MDS or AMDS according to the quantum Singleton bound under certain conditions. Some examples show that the constructed quantum codes have the better parameters than known ones maintained at [6]. Furthermore, a new class of LCD codes is given, which are almost optimal according to the sphere packing bound.
{"title":"A new class of self-orthogonal linear codes and their applications","authors":"Yaozong Zhang, Dabin Zheng, Xiaoqiang Wang","doi":"10.1016/j.disc.2025.114935","DOIUrl":"10.1016/j.disc.2025.114935","url":null,"abstract":"<div><div>Self-orthogonal codes are a subclass of linear codes that are contained within their dual codes. Since self-orthogonal codes are widely used in quantum codes, lattice theory and linear complementary dual (LCD) codes, they have received continuous attention and research. In this paper, we construct a class of self-orthogonal codes by using the defining-set approach, and determine their weight distributions and the parameters of their dual codes. Some considered codes are optimal according to the tables of best codes known maintained at <span><span>[11]</span></span> and a class of almost maximum distance separable (AMDS) codes from their duals is obtained. As applications, we obtain a class of new quantum codes, which are MDS or AMDS according to the quantum Singleton bound under certain conditions. Some examples show that the constructed quantum codes have the better parameters than known ones maintained at <span><span>[6]</span></span>. Furthermore, a new class of LCD codes is given, which are almost optimal according to the sphere packing bound.</div></div>","PeriodicalId":50572,"journal":{"name":"Discrete Mathematics","volume":"349 4","pages":"Article 114935"},"PeriodicalIF":0.7,"publicationDate":"2025-12-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145747782","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}
Boolean functions restricted to some subset of play an important role in the FLIP stream cipher proposed by Méaux et al. in 2016. Carlet et al. later studied the particular case where the subset is composed of vectors with constant Hamming weight, known as weightwise perfectly balanced (WPB) functions. Motivated by the application of nonsingular functions in stream ciphers based on feedback shift registers (FSRs), in this paper, we focus on nonsingular WPB functions. Firstly, we propose an algorithm based on the truth tables to generate all nonsingular WPB functions. A concrete construction of such functions is also provided. Considering the security in different application scenarios, we further investigate their nonlinearity and cycle structure. A tight lower bound on the nonlinearity is obtained, as well as a theoretical probability distribution of the nonlinearity. Notably, our lower bound is higher than the known lower bound on WPB functions. To generate nonsingular WPB functions with high nonlinearity, an improved algorithm is also proposed. Finally, we offer a method to analyze the cycle structure of nonsingular WPB functions, and a method to obtain such functions which generate a few cycles. Experiments show that nonsingular WPB functions are suitable for constructing de Bruijn sequences with cycle-joining method.
{"title":"On nonsingular weightwise perfectly balanced functions","authors":"Xinyi Zhao , Shizhu Tian , Xiangyong Zeng , Zhimin Sun","doi":"10.1016/j.disc.2025.114919","DOIUrl":"10.1016/j.disc.2025.114919","url":null,"abstract":"<div><div>Boolean functions restricted to some subset of <span><math><msubsup><mrow><mi>F</mi></mrow><mrow><mn>2</mn></mrow><mrow><mi>n</mi></mrow></msubsup></math></span> play an important role in the FLIP stream cipher proposed by Méaux et al. in 2016. Carlet et al. later studied the particular case where the subset is composed of vectors with constant Hamming weight, known as weightwise perfectly balanced (WPB) functions. Motivated by the application of nonsingular functions in stream ciphers based on feedback shift registers (FSRs), in this paper, we focus on nonsingular WPB functions. Firstly, we propose an algorithm based on the truth tables to generate all nonsingular WPB functions. A concrete construction of such functions is also provided. Considering the security in different application scenarios, we further investigate their nonlinearity and cycle structure. A tight lower bound on the nonlinearity is obtained, as well as a theoretical probability distribution of the nonlinearity. Notably, our lower bound is higher than the known lower bound on WPB functions. To generate nonsingular WPB functions with high nonlinearity, an improved algorithm is also proposed. Finally, we offer a method to analyze the cycle structure of nonsingular WPB functions, and a method to obtain such functions which generate a few cycles. Experiments show that nonsingular WPB functions are suitable for constructing de Bruijn sequences with cycle-joining method.</div></div>","PeriodicalId":50572,"journal":{"name":"Discrete Mathematics","volume":"349 4","pages":"Article 114919"},"PeriodicalIF":0.7,"publicationDate":"2025-12-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145693656","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}
Pub Date : 2025-12-05DOI: 10.1016/j.disc.2025.114923
Csilla Bujtás , Michael A. Henning
A set S of vertices in a graph G is a paired dominating set if every vertex of G is adjacent to a vertex in S and the subgraph induced by S admits a perfect matching. The minimum cardinality of a paired dominating set of G is the paired domination number of G. We show that if G is a graph of order n and , then .
{"title":"Paired domination in graphs with minimum degree four","authors":"Csilla Bujtás , Michael A. Henning","doi":"10.1016/j.disc.2025.114923","DOIUrl":"10.1016/j.disc.2025.114923","url":null,"abstract":"<div><div>A set <em>S</em> of vertices in a graph <em>G</em> is a paired dominating set if every vertex of <em>G</em> is adjacent to a vertex in <em>S</em> and the subgraph induced by <em>S</em> admits a perfect matching. The minimum cardinality of a paired dominating set of <em>G</em> is the paired domination number <span><math><msub><mrow><mi>γ</mi></mrow><mrow><mi>pr</mi></mrow></msub><mo>(</mo><mi>G</mi><mo>)</mo></math></span> of <em>G</em>. We show that if <em>G</em> is a graph of order <em>n</em> and <span><math><mi>δ</mi><mo>(</mo><mi>G</mi><mo>)</mo><mo>≥</mo><mn>4</mn></math></span>, then <span><math><msub><mrow><mi>γ</mi></mrow><mrow><mi>pr</mi></mrow></msub><mo>(</mo><mi>G</mi><mo>)</mo><mo>≤</mo><mfrac><mrow><mn>10</mn></mrow><mrow><mn>17</mn></mrow></mfrac><mi>n</mi><mo><</mo><mn>0.5883</mn><mi>n</mi></math></span>.</div></div>","PeriodicalId":50572,"journal":{"name":"Discrete Mathematics","volume":"349 4","pages":"Article 114923"},"PeriodicalIF":0.7,"publicationDate":"2025-12-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145693654","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}
An edge-colored graph is called rainbow if no two edges have the same color. An edge-colored graph is called properly colored if no two adjacent edges have the same color. We consider a connected edge-colored bipartite graph with bipartition in which for every color c, the set of edges colored with c forms a star. It is known that if the minimum color degree of G is at least , then G has a rainbow spanning tree. In this paper, we prove that if the minimum color degree of G is at least , then G has a rainbow spanning tree. Our theorem strengthens the previous result. We also provide a similar sufficient condition for connected edge-colored bipartite graphs to have properly colored spanning trees. Moreover, we show that these minimum color degree conditions are sharp.
{"title":"Sufficient conditions for edge-colored bipartite graphs to have rainbow and properly colored spanning trees","authors":"Shinya Fujita , Mikio Kano , Shun-ichi Maezawa , Masao Tsugaki , Kiyoshi Yoshimoto","doi":"10.1016/j.disc.2025.114921","DOIUrl":"10.1016/j.disc.2025.114921","url":null,"abstract":"<div><div>An edge-colored graph is called rainbow if no two edges have the same color. An edge-colored graph is called properly colored if no two adjacent edges have the same color. We consider a connected edge-colored bipartite graph <span><math><mi>G</mi><mo>=</mo><mi>G</mi><mo>(</mo><mi>A</mi><mo>,</mo><mi>B</mi><mo>)</mo></math></span> with bipartition <span><math><mo>(</mo><mi>A</mi><mo>,</mo><mi>B</mi><mo>)</mo></math></span> in which for every color <em>c</em>, the set of edges colored with <em>c</em> forms a star. It is known that if the minimum color degree of <em>G</em> is at least <span><math><mo>|</mo><mi>G</mi><mo>|</mo><mo>/</mo><mn>3</mn><mo>+</mo><mn>1</mn></math></span>, then <em>G</em> has a rainbow spanning tree. In this paper, we prove that if the minimum color degree of <em>G</em> is at least <span><math><mrow><mo>(</mo><mi>max</mi><mo></mo><mo>{</mo><mo>|</mo><mi>A</mi><mo>|</mo><mo>,</mo><mo>|</mo><mi>B</mi><mo>|</mo><mo>}</mo><mo>+</mo><mn>2</mn><mo>)</mo></mrow><mo>/</mo><mn>2</mn></math></span>, then <em>G</em> has a rainbow spanning tree. Our theorem strengthens the previous result. We also provide a similar sufficient condition for connected edge-colored bipartite graphs to have properly colored spanning trees. Moreover, we show that these minimum color degree conditions are sharp.</div></div>","PeriodicalId":50572,"journal":{"name":"Discrete Mathematics","volume":"349 4","pages":"Article 114921"},"PeriodicalIF":0.7,"publicationDate":"2025-12-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145693655","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}