Pub Date : 2025-12-15DOI: 10.1016/j.dam.2025.12.018
Rui Yang, Chengli Liu
A sphere is a regular planar graph whose faces are only length and length. Furthermore, it consists of exactly six length faces and even number of length faces by Euler’s formula. A graph is called cyclicallyedge-connected, if it cannot be separated into at least two components such that each contains cycles by deleting fewer than edges. We denote the maximum value of such that is cyclically edge-connected by , then the positive integer is referred to as cyclical edge-connectivity of . In this paper, we prove that the cyclical edge-connectivity of sphere is 4 or 6 or 8, and we give the structures of spheres with cyclical edge-connectivities 4 and 6, respectively. A face of is called resonant if its boundary is alternating cycle, where is a perfect matching of . Furthermore, in this paper, we show that every length face of a sphere is resonant.
{"title":"The structural properties of {(2,3),6}-spheres","authors":"Rui Yang, Chengli Liu","doi":"10.1016/j.dam.2025.12.018","DOIUrl":"10.1016/j.dam.2025.12.018","url":null,"abstract":"<div><div>A <span><math><mrow><mrow><mo>{</mo><mrow><mo>(</mo><mn>2</mn><mo>,</mo><mn>3</mn><mo>)</mo></mrow><mo>,</mo><mn>6</mn><mo>}</mo></mrow><mtext>-</mtext></mrow></math></span> sphere <span><math><mi>S</mi></math></span> is a <span><math><mrow><mn>6</mn><mtext>-</mtext></mrow></math></span>regular planar graph whose faces are only <span><math><mrow><mn>2</mn><mtext>-</mtext></mrow></math></span>length and <span><math><mrow><mn>3</mn><mtext>-</mtext></mrow></math></span>length. Furthermore, it consists of exactly six <span><math><mrow><mn>2</mn><mtext>-</mtext></mrow></math></span>length faces and even number of <span><math><mrow><mn>3</mn><mtext>-</mtext></mrow></math></span>length faces by Euler’s formula. A graph <span><math><mi>G</mi></math></span> is called <em>cyclically</em> <span><math><mrow><mi>k</mi><mtext>-</mtext></mrow></math></span><em>edge-connected</em>, if it cannot be separated into at least two components such that each contains cycles by deleting fewer than <span><math><mi>k</mi></math></span> edges. We denote the maximum value of <span><math><mrow><mi>k</mi><mo>∈</mo><mi>N</mi></mrow></math></span> such that <span><math><mi>G</mi></math></span> is cyclically <span><math><mrow><mi>k</mi><mtext>-</mtext></mrow></math></span>edge-connected by <span><math><mrow><mi>c</mi><mi>λ</mi><mrow><mo>(</mo><mi>G</mi><mo>)</mo></mrow></mrow></math></span>, then the positive integer <span><math><mrow><mi>c</mi><mi>λ</mi><mrow><mo>(</mo><mi>G</mi><mo>)</mo></mrow></mrow></math></span> is referred to as <em>cyclical edge-connectivity</em> of <span><math><mi>G</mi></math></span>. In this paper, we prove that the cyclical edge-connectivity of <span><math><mrow><mrow><mo>{</mo><mrow><mo>(</mo><mn>2</mn><mo>,</mo><mn>3</mn><mo>)</mo></mrow><mo>,</mo><mn>6</mn><mo>}</mo></mrow><mtext>-</mtext></mrow></math></span>sphere is 4 or 6 or 8, and we give the structures of <span><math><mrow><mrow><mo>{</mo><mrow><mo>(</mo><mn>2</mn><mo>,</mo><mn>3</mn><mo>)</mo></mrow><mo>,</mo><mn>6</mn><mo>}</mo></mrow><mtext>-</mtext></mrow></math></span>spheres with cyclical edge-connectivities 4 and 6, respectively. A face of <span><math><mi>G</mi></math></span> is called <em>resonant</em> if its boundary is <span><math><mrow><mi>M</mi><mtext>-</mtext></mrow></math></span>alternating cycle, where <span><math><mi>M</mi></math></span> is a perfect matching of <span><math><mi>G</mi></math></span>. Furthermore, in this paper, we show that every <span><math><mrow><mn>2</mn><mtext>-</mtext></mrow></math></span>length face of a <span><math><mrow><mrow><mo>{</mo><mrow><mo>(</mo><mn>2</mn><mo>,</mo><mn>3</mn><mo>)</mo></mrow><mo>,</mo><mn>6</mn><mo>}</mo></mrow><mtext>-</mtext></mrow></math></span>sphere is resonant.</div></div>","PeriodicalId":50573,"journal":{"name":"Discrete Applied Mathematics","volume":"383 ","pages":"Pages 15-25"},"PeriodicalIF":1.0,"publicationDate":"2025-12-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145748179","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 : 2025-12-15DOI: 10.1016/j.dam.2025.12.017
Xuelian Mao, Zhenyu Ni, Ming-Zhu Chen
For a set of graphs , a graph is called -free if it does not contain any graph in as a subgraph. Let SPEX denote the graphs with the maximum spectral radius among all -free graphs of order . In this paper, for any non-bipartite graph , we give some characterizations for the graphs in SPEX for sufficiently large , where , , and there exists at least one not equal to 3. As an application, we completely characterize the graphs in SPEX and SPEX for sufficiently large , where is a friendship graph on vertices consisting of triangles which intersect in exactly one common vertex.
对于一组图F,如果图G不包含F中的任何图作为子图,则称为F自由图。设SPEX(n,F)表示在所有n阶的F-free图中具有最大谱半径的图。在本文中,对于任意非二部图H,我们给出了对于足够大的n,其中,r≥1,k≥1,k≥2,且存在至少一个ki不等于3的SPEX(n,{∈i=1∑Pki,H})中的图的一些刻画。作为一个应用,对于足够大的n,我们完全刻画了SPEX(n,{∈i=1 l Pki,Kk+1})和SPEX(n,{∈i=1 l Pki,Fk})中的图,其中Fk是由k个恰好相交于一个公共顶点的k个三角形组成的2k+1个顶点的友谊图。
{"title":"Spectral extrema of graphs: Forbidden linear forests and non-bipartite graphs","authors":"Xuelian Mao, Zhenyu Ni, Ming-Zhu Chen","doi":"10.1016/j.dam.2025.12.017","DOIUrl":"10.1016/j.dam.2025.12.017","url":null,"abstract":"<div><div>For a set of graphs <span><math><mi>F</mi></math></span>, a graph <span><math><mi>G</mi></math></span> is called <span><math><mi>F</mi></math></span>-free if it does not contain any graph in <span><math><mi>F</mi></math></span> as a subgraph. Let SPEX<span><math><mrow><mo>(</mo><mi>n</mi><mo>,</mo><mi>F</mi><mo>)</mo></mrow></math></span> denote the graphs with the maximum spectral radius among all <span><math><mi>F</mi></math></span>-free graphs of order <span><math><mi>n</mi></math></span>. In this paper, for any non-bipartite graph <span><math><mi>H</mi></math></span>, we give some characterizations for the graphs in SPEX<span><math><mrow><mo>(</mo><mi>n</mi><mo>,</mo><mrow><mo>{</mo><msubsup><mrow><mo>⋃</mo></mrow><mrow><mi>i</mi><mo>=</mo><mn>1</mn></mrow><mrow><mi>ℓ</mi></mrow></msubsup><msub><mrow><mi>P</mi></mrow><mrow><msub><mrow><mi>k</mi></mrow><mrow><mi>i</mi></mrow></msub></mrow></msub><mo>,</mo><mi>H</mi><mo>}</mo></mrow><mo>)</mo></mrow></math></span> for sufficiently large <span><math><mi>n</mi></math></span>, where <span><math><mrow><mi>ℓ</mi><mo>≥</mo><mn>1</mn></mrow></math></span>, <span><math><mrow><msub><mrow><mi>k</mi></mrow><mrow><mn>1</mn></mrow></msub><mo>≥</mo><mo>⋯</mo><mo>≥</mo><msub><mrow><mi>k</mi></mrow><mrow><mi>ℓ</mi></mrow></msub><mo>≥</mo><mn>2</mn></mrow></math></span>, and there exists at least one <span><math><msub><mrow><mi>k</mi></mrow><mrow><mi>i</mi></mrow></msub></math></span> not equal to 3. As an application, we completely characterize the graphs in SPEX<span><math><mrow><mo>(</mo><mi>n</mi><mo>,</mo><mrow><mo>{</mo><msubsup><mrow><mo>⋃</mo></mrow><mrow><mi>i</mi><mo>=</mo><mn>1</mn></mrow><mrow><mi>ℓ</mi></mrow></msubsup><msub><mrow><mi>P</mi></mrow><mrow><msub><mrow><mi>k</mi></mrow><mrow><mi>i</mi></mrow></msub></mrow></msub><mo>,</mo><msub><mrow><mi>K</mi></mrow><mrow><mi>k</mi><mo>+</mo><mn>1</mn></mrow></msub><mo>}</mo></mrow><mo>)</mo></mrow></math></span> and SPEX<span><math><mrow><mo>(</mo><mi>n</mi><mo>,</mo><mrow><mo>{</mo><msubsup><mrow><mo>⋃</mo></mrow><mrow><mi>i</mi><mo>=</mo><mn>1</mn></mrow><mrow><mi>ℓ</mi></mrow></msubsup><msub><mrow><mi>P</mi></mrow><mrow><msub><mrow><mi>k</mi></mrow><mrow><mi>i</mi></mrow></msub></mrow></msub><mo>,</mo><msub><mrow><mi>F</mi></mrow><mrow><mi>k</mi></mrow></msub><mo>}</mo></mrow><mo>)</mo></mrow></math></span> for sufficiently large <span><math><mi>n</mi></math></span>, where <span><math><msub><mrow><mi>F</mi></mrow><mrow><mi>k</mi></mrow></msub></math></span> is a friendship graph on <span><math><mrow><mn>2</mn><mi>k</mi><mo>+</mo><mn>1</mn></mrow></math></span> vertices consisting of <span><math><mi>k</mi></math></span> triangles which intersect in exactly one common vertex.</div></div>","PeriodicalId":50573,"journal":{"name":"Discrete Applied Mathematics","volume":"383 ","pages":"Pages 8-14"},"PeriodicalIF":1.0,"publicationDate":"2025-12-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145748178","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 : 2025-12-15DOI: 10.1016/j.dam.2025.12.031
Jing Lin , Huawen Ma
<div><div>A celebrated result of Stiebitz asserts that for positive integers <span><math><mi>s</mi></math></span> and <span><math><mi>t</mi></math></span>, each graph <span><math><mi>G</mi></math></span> with minimum degree <span><math><mrow><mi>s</mi><mo>+</mo><mi>t</mi><mo>+</mo><mn>1</mn></mrow></math></span> can be partitioned into vertex disjoint subgraphs <span><math><msub><mrow><mi>G</mi></mrow><mrow><mn>1</mn></mrow></msub></math></span> and <span><math><msub><mrow><mi>G</mi></mrow><mrow><mn>2</mn></mrow></msub></math></span> such that <span><math><msub><mrow><mi>G</mi></mrow><mrow><mn>1</mn></mrow></msub></math></span> has minimum degree at least <span><math><mi>s</mi></math></span> and <span><math><msub><mrow><mi>G</mi></mrow><mrow><mn>2</mn></mrow></msub></math></span> has minimum degree at least <span><math><mi>t</mi></math></span>. Fujita et al. (2019) conjectured that the partition of Stiebitz can be extended to edge-colored graphs. Let <span><math><mrow><mi>G</mi><mo>=</mo><mrow><mo>(</mo><mi>V</mi><mo>,</mo><mi>E</mi><mo>,</mo><mi>c</mi><mo>)</mo></mrow></mrow></math></span> be a graph, where <span><math><mi>c</mi></math></span> is an edge coloring of <span><math><mi>G</mi></math></span>. For a vertex <span><math><mi>v</mi></math></span> of <span><math><mi>G</mi></math></span>, let <span><math><mrow><mi>E</mi><mrow><mo>(</mo><mi>v</mi><mo>)</mo></mrow></mrow></math></span> denote the edges of <span><math><mi>G</mi></math></span> incident to <span><math><mi>v</mi></math></span>, let <span><math><mrow><mi>d</mi><mrow><mo>(</mo><mi>v</mi><mo>)</mo></mrow><mo>=</mo><mrow><mo>|</mo><mi>E</mi><mrow><mo>(</mo><mi>v</mi><mo>)</mo></mrow><mo>|</mo></mrow></mrow></math></span> be the degree of <span><math><mi>v</mi></math></span> in <span><math><mi>G</mi></math></span>, let <span><math><mrow><mi>c</mi><mrow><mo>(</mo><mi>E</mi><mrow><mo>(</mo><mi>v</mi><mo>)</mo></mrow><mo>)</mo></mrow></mrow></math></span> be the color set which contains all colors appearing on <span><math><mrow><mi>E</mi><mrow><mo>(</mo><mi>v</mi><mo>)</mo></mrow></mrow></math></span> and let <span><math><mrow><msup><mrow><mi>d</mi></mrow><mrow><mi>c</mi></mrow></msup><mrow><mo>(</mo><mi>v</mi><mo>)</mo></mrow><mo>=</mo><mrow><mo>|</mo><mi>c</mi><mrow><mo>(</mo><mi>E</mi><mrow><mo>(</mo><mi>v</mi><mo>)</mo></mrow><mo>)</mo></mrow><mo>|</mo></mrow></mrow></math></span> be the color degree of <span><math><mi>v</mi></math></span> in <span><math><mi>G</mi></math></span>. Furthermore, let <span><math><mrow><msup><mrow><mi>δ</mi></mrow><mrow><mi>c</mi></mrow></msup><mrow><mo>(</mo><mi>G</mi><mo>)</mo></mrow><mo>=</mo><mo>min</mo><mrow><mo>{</mo><msup><mrow><mi>d</mi></mrow><mrow><mi>c</mi></mrow></msup><mrow><mo>(</mo><mi>v</mi><mo>)</mo></mrow><mo>∣</mo><mi>v</mi><mo>∈</mo><mi>V</mi><mrow><mo>(</mo><mi>G</mi><mo>)</mo></mrow><mo>}</mo></mrow></mrow></math></span> be the minimum color degree of <span><math><mi>G</mi></math></span> (with respect to <span><math><mi>c</mi></math><
Stiebitz的一个著名结果断言,对于正整数s和t,每个最小度为s+t+1的图G都可以划分为顶点不相交子图G1和G2,使得G1的最小度至少为s, G2的最小度至少为t。Fujita et al.(2019)推测Stiebitz的划分可以推广到边色图。让G = (V, E、c)是一个图表,其中c是一个边缘着色G的顶点V (G)让E (V)表示G事件V的边缘,让d (V) = | E (V) | G V的程度,让c (E (V))的颜色集包含所有颜色出现在E (V)和直流(V) = | c (E (V) |在G .此外,V的颜色程度让δc (G) =分钟{直流(V)∣V∈V (G)}是最低程度的颜色G(关于c)。当δc(G[S])≥S且δc(G[T])≥T时,V(G)的分割(S,T)是(S,T)可行的。其中G[U]表示顶点集U诱导出的G的子图。Fujita、Li和Wang推测,在δc(G)≥s+t+1和s≥t≥2的条件下,G具有(s,t)可行划分。本文证明了如果s≥t≥2,且对于每个v∈v (G), G具有(s,t)可行分割,且满足以下三个条件之一:(1)2dc(v)−d(v)≥s+t+1。(2) dc(v)≥ks+t+1,对于每个v∈v (G), G相对于c的每个色类最大度数不超过k。(3)dc(v)≥s+t+1,对于每个v∈v (G), c是传递着色(即如果P=(u,v,w)是G中的路径,且c(uv)=c(vw),则uw∈E(G), c(uv)=c(vw))。
{"title":"On partitions of edge-colored graphs under color degree constraints","authors":"Jing Lin , Huawen Ma","doi":"10.1016/j.dam.2025.12.031","DOIUrl":"10.1016/j.dam.2025.12.031","url":null,"abstract":"<div><div>A celebrated result of Stiebitz asserts that for positive integers <span><math><mi>s</mi></math></span> and <span><math><mi>t</mi></math></span>, each graph <span><math><mi>G</mi></math></span> with minimum degree <span><math><mrow><mi>s</mi><mo>+</mo><mi>t</mi><mo>+</mo><mn>1</mn></mrow></math></span> can be partitioned into vertex disjoint subgraphs <span><math><msub><mrow><mi>G</mi></mrow><mrow><mn>1</mn></mrow></msub></math></span> and <span><math><msub><mrow><mi>G</mi></mrow><mrow><mn>2</mn></mrow></msub></math></span> such that <span><math><msub><mrow><mi>G</mi></mrow><mrow><mn>1</mn></mrow></msub></math></span> has minimum degree at least <span><math><mi>s</mi></math></span> and <span><math><msub><mrow><mi>G</mi></mrow><mrow><mn>2</mn></mrow></msub></math></span> has minimum degree at least <span><math><mi>t</mi></math></span>. Fujita et al. (2019) conjectured that the partition of Stiebitz can be extended to edge-colored graphs. Let <span><math><mrow><mi>G</mi><mo>=</mo><mrow><mo>(</mo><mi>V</mi><mo>,</mo><mi>E</mi><mo>,</mo><mi>c</mi><mo>)</mo></mrow></mrow></math></span> be a graph, where <span><math><mi>c</mi></math></span> is an edge coloring of <span><math><mi>G</mi></math></span>. For a vertex <span><math><mi>v</mi></math></span> of <span><math><mi>G</mi></math></span>, let <span><math><mrow><mi>E</mi><mrow><mo>(</mo><mi>v</mi><mo>)</mo></mrow></mrow></math></span> denote the edges of <span><math><mi>G</mi></math></span> incident to <span><math><mi>v</mi></math></span>, let <span><math><mrow><mi>d</mi><mrow><mo>(</mo><mi>v</mi><mo>)</mo></mrow><mo>=</mo><mrow><mo>|</mo><mi>E</mi><mrow><mo>(</mo><mi>v</mi><mo>)</mo></mrow><mo>|</mo></mrow></mrow></math></span> be the degree of <span><math><mi>v</mi></math></span> in <span><math><mi>G</mi></math></span>, let <span><math><mrow><mi>c</mi><mrow><mo>(</mo><mi>E</mi><mrow><mo>(</mo><mi>v</mi><mo>)</mo></mrow><mo>)</mo></mrow></mrow></math></span> be the color set which contains all colors appearing on <span><math><mrow><mi>E</mi><mrow><mo>(</mo><mi>v</mi><mo>)</mo></mrow></mrow></math></span> and let <span><math><mrow><msup><mrow><mi>d</mi></mrow><mrow><mi>c</mi></mrow></msup><mrow><mo>(</mo><mi>v</mi><mo>)</mo></mrow><mo>=</mo><mrow><mo>|</mo><mi>c</mi><mrow><mo>(</mo><mi>E</mi><mrow><mo>(</mo><mi>v</mi><mo>)</mo></mrow><mo>)</mo></mrow><mo>|</mo></mrow></mrow></math></span> be the color degree of <span><math><mi>v</mi></math></span> in <span><math><mi>G</mi></math></span>. Furthermore, let <span><math><mrow><msup><mrow><mi>δ</mi></mrow><mrow><mi>c</mi></mrow></msup><mrow><mo>(</mo><mi>G</mi><mo>)</mo></mrow><mo>=</mo><mo>min</mo><mrow><mo>{</mo><msup><mrow><mi>d</mi></mrow><mrow><mi>c</mi></mrow></msup><mrow><mo>(</mo><mi>v</mi><mo>)</mo></mrow><mo>∣</mo><mi>v</mi><mo>∈</mo><mi>V</mi><mrow><mo>(</mo><mi>G</mi><mo>)</mo></mrow><mo>}</mo></mrow></mrow></math></span> be the minimum color degree of <span><math><mi>G</mi></math></span> (with respect to <span><math><mi>c</mi></math><","PeriodicalId":50573,"journal":{"name":"Discrete Applied Mathematics","volume":"383 ","pages":"Pages 1-7"},"PeriodicalIF":1.0,"publicationDate":"2025-12-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145750379","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 : 2025-12-15DOI: 10.1016/j.dam.2025.12.011
Olivier Baudon , Julien Bensmail , Morgan Boivin , Igor Grzelec , Clara Marcille
The Strong -Conjecture asks whether, for all connected graphs different from and , we can assign to edges red and blue labels with value 1 or 2 so that no two adjacent vertices have the same sum of incident red labels or the same sum of incident blue labels. This conjecture, which can be perceived as a generalisation of the so-called 1–2–3 Conjecture, as, thus far, been proved only for a handful number of graph classes. In this work, we prove the Strong -Conjecture holds for more classes of graphs. In particular, we prove the conjecture for cacti, subcubic outerplanar graphs, graphs with maximum average degree less than , and some Halin graphs, among others.
{"title":"The strong (2,2)-Conjecture for more classes of graphs","authors":"Olivier Baudon , Julien Bensmail , Morgan Boivin , Igor Grzelec , Clara Marcille","doi":"10.1016/j.dam.2025.12.011","DOIUrl":"10.1016/j.dam.2025.12.011","url":null,"abstract":"<div><div>The Strong <span><math><mrow><mo>(</mo><mn>2</mn><mo>,</mo><mn>2</mn><mo>)</mo></mrow></math></span>-Conjecture asks whether, for all connected graphs different from <span><math><msub><mrow><mi>K</mi></mrow><mrow><mn>2</mn></mrow></msub></math></span> and <span><math><msub><mrow><mi>K</mi></mrow><mrow><mn>3</mn></mrow></msub></math></span>, we can assign to edges red and blue labels with value 1 or 2 so that no two adjacent vertices have the same sum of incident red labels or the same sum of incident blue labels. This conjecture, which can be perceived as a generalisation of the so-called 1–2–3 Conjecture, as, thus far, been proved only for a handful number of graph classes. In this work, we prove the Strong <span><math><mrow><mo>(</mo><mn>2</mn><mo>,</mo><mn>2</mn><mo>)</mo></mrow></math></span>-Conjecture holds for more classes of graphs. In particular, we prove the conjecture for cacti, subcubic outerplanar graphs, graphs with maximum average degree less than <span><math><mfrac><mrow><mn>9</mn></mrow><mrow><mn>4</mn></mrow></mfrac></math></span>, and some Halin graphs, among others.</div></div>","PeriodicalId":50573,"journal":{"name":"Discrete Applied Mathematics","volume":"382 ","pages":"Pages 337-354"},"PeriodicalIF":1.0,"publicationDate":"2025-12-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145790312","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}
Csáji, Jungers, and Blondel prove that while a PageRank optimization problem with edge selection constraints is NP-hard, it can be solved optimally in polynomial time for the unconstrained case. This theoretical result is accompanied by several observations, which we leverage to develop valid inequalities in polynomial time for this class of NP-hard problems. We show that these observations can be exploited to derive stronger inequalities than the standard valid inequality available in the literature. These valid inequalities provide a theoretical basis for reducing the optimality gap of the constrained PageRank problem without changing NP-hardness.
{"title":"A note on valid inequalities for PageRank optimization with edge selection constraints","authors":"Shang-Ru Yang, Yung-Han Liao, Chih-Ching Chien, Hao-Hsiang Wu","doi":"10.1016/j.dam.2025.12.023","DOIUrl":"10.1016/j.dam.2025.12.023","url":null,"abstract":"<div><div>Csáji, Jungers, and Blondel prove that while a PageRank optimization problem with edge selection constraints is NP-hard, it can be solved optimally in polynomial time for the unconstrained case. This theoretical result is accompanied by several observations, which we leverage to develop valid inequalities in polynomial time for this class of NP-hard problems. We show that these observations can be exploited to derive stronger inequalities than the standard valid inequality available in the literature. These valid inequalities provide a theoretical basis for reducing the optimality gap of the constrained PageRank problem without changing NP-hardness.</div></div>","PeriodicalId":50573,"journal":{"name":"Discrete Applied Mathematics","volume":"383 ","pages":"Pages 44-51"},"PeriodicalIF":1.0,"publicationDate":"2025-12-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145792198","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 : 2025-12-15DOI: 10.1016/j.dam.2025.12.001
Kanstantsin Pashkovich, Alice Sayutina
We consider the matroid prophet inequality problem. This problem has been extensively studied in the case of adaptive mechanisms. In particular, there is a tight 2-competitive mechanism for all matroids (Kleinberg and Weinberg, 2012).
However, it is not known what classes of matroids admit non-adaptive mechanisms with constant guarantee. Recently, in Chawla et al. (2024) it was shown that there are constant-competitive non-adaptive mechanisms for graphic matroids. In this work, we show that various known classes of matroids admit constant-competitive non-adaptive mechanisms.
{"title":"Non-adaptive prophet inequalities for minor-closed classes of matroids","authors":"Kanstantsin Pashkovich, Alice Sayutina","doi":"10.1016/j.dam.2025.12.001","DOIUrl":"10.1016/j.dam.2025.12.001","url":null,"abstract":"<div><div>We consider the matroid prophet inequality problem. This problem has been extensively studied in the case of adaptive mechanisms. In particular, there is a tight 2-competitive mechanism for all matroids (Kleinberg and Weinberg, 2012).</div><div>However, it is not known what classes of matroids admit non-adaptive mechanisms with constant guarantee. Recently, in Chawla et al. (2024) it was shown that there are constant-competitive non-adaptive mechanisms for graphic matroids. In this work, we show that various known classes of matroids admit constant-competitive non-adaptive mechanisms.</div></div>","PeriodicalId":50573,"journal":{"name":"Discrete Applied Mathematics","volume":"383 ","pages":"Pages 26-43"},"PeriodicalIF":1.0,"publicationDate":"2025-12-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145748180","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 : 2025-12-13DOI: 10.1016/j.dam.2025.12.015
Gabriela Araujo-Pardo , Martín Matamala , Juan Pablo Peña , José Zamora
A set of non-collinear points in the Euclidean plane defines at least different lines. Chen and Chvátal in 2008 conjectured that the same result is true in metric spaces for an adequate definition of line. More recently, it was conjectured in 2018 by Aboulker et al. that any large enough bridgeless graph on vertices defines a metric space that has at least lines.
We study the natural extension of Aboulker et al.’s conjecture into the context of quasi-metric spaces defined by digraphs of low diameter. We prove that it is valid for quasi-metric spaces defined by bipartite digraphs of diameter at most three, oriented graphs of diameter two and, digraphs of diameter three and directed girth four.
{"title":"Lines on digraphs of low diameter","authors":"Gabriela Araujo-Pardo , Martín Matamala , Juan Pablo Peña , José Zamora","doi":"10.1016/j.dam.2025.12.015","DOIUrl":"10.1016/j.dam.2025.12.015","url":null,"abstract":"<div><div>A set of <span><math><mi>n</mi></math></span> non-collinear points in the Euclidean plane defines at least <span><math><mi>n</mi></math></span> different lines. Chen and Chvátal in 2008 conjectured that the same result is true in metric spaces for an adequate definition of line. More recently, it was conjectured in 2018 by Aboulker et al. that any large enough bridgeless graph on <span><math><mi>n</mi></math></span> vertices defines a metric space that has at least <span><math><mi>n</mi></math></span> lines.</div><div>We study the natural extension of Aboulker et al.’s conjecture into the context of quasi-metric spaces defined by digraphs of low diameter. We prove that it is valid for quasi-metric spaces defined by bipartite digraphs of diameter at most three, oriented graphs of diameter two and, digraphs of diameter three and directed girth four.</div></div>","PeriodicalId":50573,"journal":{"name":"Discrete Applied Mathematics","volume":"382 ","pages":"Pages 293-300"},"PeriodicalIF":1.0,"publicationDate":"2025-12-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145737341","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 : 2025-12-12DOI: 10.1016/j.dam.2025.12.010
Ayun Zhang , Baoleer , Shinya Fujita , Yaping Mao , Gang Yang
<div><div>An <em>ordered graph</em> is a pair <span><math><mrow><msup><mrow><mi>G</mi></mrow><mrow><mo>≺</mo></mrow></msup><mo>=</mo><mrow><mo>(</mo><mi>G</mi><mo>,</mo><mo>≺</mo><mo>)</mo></mrow></mrow></math></span>, where <span><math><mo>≺</mo></math></span> is a total ordering of the vertex set <span><math><mrow><mi>V</mi><mrow><mo>(</mo><mi>G</mi><mo>)</mo></mrow></mrow></math></span>. In this paper, we define a <em>bip-ordered bipartite graph</em> as a pair <span><math><mrow><msup><mrow><mi>G</mi></mrow><mrow><mo><</mo></mrow></msup><mo>=</mo><mrow><mo>(</mo><mi>G</mi><mo>,</mo><mo><</mo><mo>)</mo></mrow></mrow></math></span>, where <span><math><mrow><mi>G</mi><mo>=</mo><mrow><mo>(</mo><mi>X</mi><mo>,</mo><mi>Y</mi><mo>,</mo><mi>E</mi><mo>)</mo></mrow></mrow></math></span> is a bipartite graph and where <span><math><mo><</mo></math></span> is a <em>bip-order</em> (for bipartite-order), namely, <span><math><mo><</mo></math></span> is a total bip-order on <span><math><mrow><mi>V</mi><mrow><mo>(</mo><mi>G</mi><mo>)</mo></mrow><mo>=</mo><mi>X</mi><mo>∪</mo><mi>Y</mi></mrow></math></span> such that every vertex of <span><math><mi>X</mi></math></span> precedes every vertex of <span><math><mi>Y</mi></math></span> (that is, <span><math><mrow><mi>x</mi><mo><</mo><mi>y</mi></mrow></math></span>, for any <span><math><mrow><mrow><mo>(</mo><mi>x</mi><mo>,</mo><mi>y</mi><mo>)</mo></mrow><mo>∈</mo><mi>X</mi><mo>×</mo><mi>Y</mi></mrow></math></span>). For bip-ordered bipartite graphs <span><math><mrow><msubsup><mrow><mi>G</mi></mrow><mrow><mn>1</mn></mrow><mrow><mo><</mo></mrow></msubsup><mo>,</mo><mo>…</mo><mo>,</mo><msubsup><mrow><mi>G</mi></mrow><mrow><mi>k</mi></mrow><mrow><mo><</mo></mrow></msubsup></mrow></math></span>, the <em>bip-ordered bipartite Ramsey number</em> <span><math><mrow><mover><mrow><mi>b</mi><mi>b</mi><mi>r</mi></mrow><mo>¯</mo></mover><mrow><mo>(</mo><msubsup><mrow><mi>G</mi></mrow><mrow><mn>1</mn></mrow><mrow><mo><</mo></mrow></msubsup><mo>,</mo><mo>…</mo><mo>,</mo><msubsup><mrow><mi>G</mi></mrow><mrow><mi>k</mi></mrow><mrow><mo><</mo></mrow></msubsup><mo>)</mo></mrow></mrow></math></span> is the least positive integer <span><math><mi>N</mi></math></span> for which the following property holds: for any <span><math><mi>k</mi></math></span>-edge-coloring of <span><math><msubsup><mrow><mi>K</mi></mrow><mrow><mi>N</mi><mo>,</mo><mi>N</mi></mrow><mrow><mo><</mo></mrow></msubsup></math></span>, there is a color <span><math><mrow><mi>i</mi><mo>∈</mo><mrow><mo>{</mo><mn>1</mn><mo>,</mo><mo>…</mo><mo>,</mo><mi>k</mi><mo>}</mo></mrow></mrow></math></span>, such that the subgraph of <span><math><msubsup><mrow><mi>K</mi></mrow><mrow><mi>N</mi><mo>,</mo><mi>N</mi></mrow><mrow><mo><</mo></mrow></msubsup></math></span> induced by edges of color <span><math><mi>i</mi></math></span> contains a copy of <span><math><msubsup><mrow><mi>G</mi></mrow><mrow><mi>i</mi></mrow><mrow><mo><</mo></mrow></msubsup></math></span
{"title":"Bip-ordered bipartite Ramsey number","authors":"Ayun Zhang , Baoleer , Shinya Fujita , Yaping Mao , Gang Yang","doi":"10.1016/j.dam.2025.12.010","DOIUrl":"10.1016/j.dam.2025.12.010","url":null,"abstract":"<div><div>An <em>ordered graph</em> is a pair <span><math><mrow><msup><mrow><mi>G</mi></mrow><mrow><mo>≺</mo></mrow></msup><mo>=</mo><mrow><mo>(</mo><mi>G</mi><mo>,</mo><mo>≺</mo><mo>)</mo></mrow></mrow></math></span>, where <span><math><mo>≺</mo></math></span> is a total ordering of the vertex set <span><math><mrow><mi>V</mi><mrow><mo>(</mo><mi>G</mi><mo>)</mo></mrow></mrow></math></span>. In this paper, we define a <em>bip-ordered bipartite graph</em> as a pair <span><math><mrow><msup><mrow><mi>G</mi></mrow><mrow><mo><</mo></mrow></msup><mo>=</mo><mrow><mo>(</mo><mi>G</mi><mo>,</mo><mo><</mo><mo>)</mo></mrow></mrow></math></span>, where <span><math><mrow><mi>G</mi><mo>=</mo><mrow><mo>(</mo><mi>X</mi><mo>,</mo><mi>Y</mi><mo>,</mo><mi>E</mi><mo>)</mo></mrow></mrow></math></span> is a bipartite graph and where <span><math><mo><</mo></math></span> is a <em>bip-order</em> (for bipartite-order), namely, <span><math><mo><</mo></math></span> is a total bip-order on <span><math><mrow><mi>V</mi><mrow><mo>(</mo><mi>G</mi><mo>)</mo></mrow><mo>=</mo><mi>X</mi><mo>∪</mo><mi>Y</mi></mrow></math></span> such that every vertex of <span><math><mi>X</mi></math></span> precedes every vertex of <span><math><mi>Y</mi></math></span> (that is, <span><math><mrow><mi>x</mi><mo><</mo><mi>y</mi></mrow></math></span>, for any <span><math><mrow><mrow><mo>(</mo><mi>x</mi><mo>,</mo><mi>y</mi><mo>)</mo></mrow><mo>∈</mo><mi>X</mi><mo>×</mo><mi>Y</mi></mrow></math></span>). For bip-ordered bipartite graphs <span><math><mrow><msubsup><mrow><mi>G</mi></mrow><mrow><mn>1</mn></mrow><mrow><mo><</mo></mrow></msubsup><mo>,</mo><mo>…</mo><mo>,</mo><msubsup><mrow><mi>G</mi></mrow><mrow><mi>k</mi></mrow><mrow><mo><</mo></mrow></msubsup></mrow></math></span>, the <em>bip-ordered bipartite Ramsey number</em> <span><math><mrow><mover><mrow><mi>b</mi><mi>b</mi><mi>r</mi></mrow><mo>¯</mo></mover><mrow><mo>(</mo><msubsup><mrow><mi>G</mi></mrow><mrow><mn>1</mn></mrow><mrow><mo><</mo></mrow></msubsup><mo>,</mo><mo>…</mo><mo>,</mo><msubsup><mrow><mi>G</mi></mrow><mrow><mi>k</mi></mrow><mrow><mo><</mo></mrow></msubsup><mo>)</mo></mrow></mrow></math></span> is the least positive integer <span><math><mi>N</mi></math></span> for which the following property holds: for any <span><math><mi>k</mi></math></span>-edge-coloring of <span><math><msubsup><mrow><mi>K</mi></mrow><mrow><mi>N</mi><mo>,</mo><mi>N</mi></mrow><mrow><mo><</mo></mrow></msubsup></math></span>, there is a color <span><math><mrow><mi>i</mi><mo>∈</mo><mrow><mo>{</mo><mn>1</mn><mo>,</mo><mo>…</mo><mo>,</mo><mi>k</mi><mo>}</mo></mrow></mrow></math></span>, such that the subgraph of <span><math><msubsup><mrow><mi>K</mi></mrow><mrow><mi>N</mi><mo>,</mo><mi>N</mi></mrow><mrow><mo><</mo></mrow></msubsup></math></span> induced by edges of color <span><math><mi>i</mi></math></span> contains a copy of <span><math><msubsup><mrow><mi>G</mi></mrow><mrow><mi>i</mi></mrow><mrow><mo><</mo></mrow></msubsup></math></span","PeriodicalId":50573,"journal":{"name":"Discrete Applied Mathematics","volume":"382 ","pages":"Pages 327-336"},"PeriodicalIF":1.0,"publicationDate":"2025-12-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145737338","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 : 2025-12-12DOI: 10.1016/j.dam.2025.12.009
Peter Damaschke , Karinne Ramirez-Amaro
Suppose that we are given a finite set of Boolean attributes and a set of actions defined on them. Every action has the effect of changing some attribute values and may also depend on further attribute values which are, however, not changed. The subset of attributes affected by an action is known as precondition. The goal is to find some sequence of executable actions that transform a given initial state into a desired target state. This type of problem appears, e.g., in robot motion planning. In this paper, we study cases of the problem where the precondition of every action only depends on a conjunction of terms with at most two attributes. We classify a number of cases as polynomial-time solvable or NP-complete. They amount to extended versions of some classic graph problems, among them topological orderings and perfect matchings. This appears to be the first systematic study of preconditions, despite the rich literature on many aspects of path finding in finite state spaces. A complete dichotomy of polynomial-time and NP-complete cases remains an open question.
{"title":"Complexity of action path finding with small precondition sets","authors":"Peter Damaschke , Karinne Ramirez-Amaro","doi":"10.1016/j.dam.2025.12.009","DOIUrl":"10.1016/j.dam.2025.12.009","url":null,"abstract":"<div><div>Suppose that we are given a finite set of Boolean attributes and a set of actions defined on them. Every action has the effect of changing some attribute values and may also depend on further attribute values which are, however, not changed. The subset of attributes affected by an action is known as precondition. The goal is to find some sequence of executable actions that transform a given initial state into a desired target state. This type of problem appears, e.g., in robot motion planning. In this paper, we study cases of the problem where the precondition of every action only depends on a conjunction of terms with at most two attributes. We classify a number of cases as polynomial-time solvable or NP-complete. They amount to extended versions of some classic graph problems, among them topological orderings and perfect matchings. This appears to be the first systematic study of preconditions, despite the rich literature on many aspects of path finding in finite state spaces. A complete dichotomy of polynomial-time and NP-complete cases remains an open question.</div></div>","PeriodicalId":50573,"journal":{"name":"Discrete Applied Mathematics","volume":"381 ","pages":"Pages 339-348"},"PeriodicalIF":1.0,"publicationDate":"2025-12-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145790231","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 : 2025-12-12DOI: 10.1016/j.dam.2025.12.021
Ioan Tomescu
The bond incident degree (BID) index of a connected graph with edge-weight function is defined as where is a symmetric real function with and and is the degree of vertex in . In this paper, we find extremal trees and unicyclic graphs of order with given maximum degree having maximum bond incident degree index if edge-weight symmetric function satisfies five conditions. These conditions are fulfilled by sum-connectivity index, general sum-connectivity index, modified Sombor index and harmonic index.
{"title":"Maximum bond incident degree indices for trees and unicyclic graphs with given maximum degree","authors":"Ioan Tomescu","doi":"10.1016/j.dam.2025.12.021","DOIUrl":"10.1016/j.dam.2025.12.021","url":null,"abstract":"<div><div>The bond incident degree (BID) index <span><math><mrow><msub><mrow><mi>T</mi></mrow><mrow><mi>f</mi></mrow></msub><mrow><mo>(</mo><mi>G</mi><mo>)</mo></mrow></mrow></math></span> of a connected graph <span><math><mi>G</mi></math></span> with edge-weight function <span><math><mrow><mi>f</mi><mrow><mo>(</mo><mi>x</mi><mo>,</mo><mi>y</mi><mo>)</mo></mrow></mrow></math></span> is defined as <span><math><mrow><msub><mrow><mi>T</mi></mrow><mrow><mi>f</mi></mrow></msub><mrow><mo>(</mo><mi>G</mi><mo>)</mo></mrow><mo>=</mo><munder><mrow><mo>∑</mo></mrow><mrow><msub><mrow><mi>v</mi></mrow><mrow><mi>i</mi></mrow></msub><msub><mrow><mi>v</mi></mrow><mrow><mi>j</mi></mrow></msub><mo>∈</mo><mi>E</mi><mrow><mo>(</mo><mi>G</mi><mo>)</mo></mrow></mrow></munder><mi>f</mi><mrow><mo>(</mo><mi>d</mi><mrow><mo>(</mo><msub><mrow><mi>v</mi></mrow><mrow><mi>i</mi></mrow></msub><mo>)</mo></mrow><mo>,</mo><mi>d</mi><mrow><mo>(</mo><msub><mrow><mi>v</mi></mrow><mrow><mi>j</mi></mrow></msub><mo>)</mo></mrow><mo>)</mo></mrow><mo>,</mo></mrow></math></span> where <span><math><mrow><mi>f</mi><mrow><mo>(</mo><mi>x</mi><mo>,</mo><mi>y</mi><mo>)</mo></mrow><mo>></mo><mn>0</mn></mrow></math></span> is a symmetric real function with <span><math><mrow><mi>x</mi><mo>≥</mo><mn>1</mn></mrow></math></span> and <span><math><mrow><mi>y</mi><mo>≥</mo><mn>1</mn></mrow></math></span> and <span><math><mrow><mi>d</mi><mrow><mo>(</mo><mi>u</mi><mo>)</mo></mrow></mrow></math></span> is the degree of vertex <span><math><mi>u</mi></math></span> in <span><math><mi>G</mi></math></span>. In this paper, we find extremal trees and unicyclic graphs of order <span><math><mi>n</mi></math></span> with given maximum degree having maximum bond incident degree index <span><math><msub><mrow><mi>T</mi></mrow><mrow><mi>f</mi></mrow></msub></math></span> if edge-weight symmetric function <span><math><mrow><mi>f</mi><mrow><mo>(</mo><mi>x</mi><mo>,</mo><mi>y</mi><mo>)</mo></mrow></mrow></math></span> satisfies five conditions. These conditions are fulfilled by sum-connectivity index, general sum-connectivity index, modified Sombor index and harmonic index.</div></div>","PeriodicalId":50573,"journal":{"name":"Discrete Applied Mathematics","volume":"382 ","pages":"Pages 272-276"},"PeriodicalIF":1.0,"publicationDate":"2025-12-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145737326","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}