Discrete Optimization最新文献

{"title":"Packing mixed hyperarborescences","authors":"Zoltán Szigeti","doi":"10.1016/j.disopt.2023.100811","DOIUrl":"10.1016/j.disopt.2023.100811","url":null,"abstract":"<div><p><span>The aim of this paper is twofold. We first provide a new orientation theorem which gives a natural and simple proof of a result of Gao and Yang (2021) on matroid-reachability-based packing of mixed arborescences in mixed graphs by reducing it to the corresponding theorem of Király (2016) on directed graphs. Moreover, we extend another result of Gao and Yang (2021) by providing a new theorem on mixed hypergraphs having a packing of mixed hyperarborescences such that their number is at least </span><span><math><mi>ℓ</mi></math></span> and at most <span><math><msup><mrow><mi>ℓ</mi></mrow><mrow><mo>′</mo></mrow></msup></math></span>, each vertex belongs to exactly <span><math><mi>k</mi></math></span> of them, and each vertex <span><math><mi>v</mi></math></span> is the root of least <span><math><mrow><mi>f</mi><mrow><mo>(</mo><mi>v</mi><mo>)</mo></mrow></mrow></math></span> and at most <span><math><mrow><mi>g</mi><mrow><mo>(</mo><mi>v</mi><mo>)</mo></mrow></mrow></math></span> of them.</p></div>","PeriodicalId":50571,"journal":{"name":"Discrete Optimization","volume":null,"pages":null},"PeriodicalIF":1.1,"publicationDate":"2023-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136102757","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The maximum number of short paths in a Halin graph","authors":"Shunhai He ,&nbsp;Huiqing Liu","doi":"10.1016/j.disopt.2023.100809","DOIUrl":"https://doi.org/10.1016/j.disopt.2023.100809","url":null,"abstract":"<div><p>A Halin graph <span><math><mi>G</mi></math></span> is a plane graph consisting of a plane embedding of a tree <span><math><mi>T</mi></math></span> of order at least 4 containing no vertex of degree 2, and of a cycle <span><math><mi>C</mi></math></span> connecting all leaves of <span><math><mi>T</mi></math></span>. Let <span><math><mrow><msub><mrow><mi>f</mi></mrow><mrow><mi>h</mi></mrow></msub><mrow><mo>(</mo><mi>n</mi><mo>,</mo><mi>G</mi><mo>)</mo></mrow></mrow></math></span> be the maximum number of copies of <span><math><mi>G</mi></math></span> in a Halin graph on <span><math><mi>n</mi></math></span> vertices. In this paper, we give exact values of <span><math><mrow><msub><mrow><mi>f</mi></mrow><mrow><mi>h</mi></mrow></msub><mrow><mo>(</mo><mi>n</mi><mo>,</mo><mi>G</mi><mo>)</mo></mrow></mrow></math></span> when <span><math><mi>G</mi></math></span> is a path on <span><math><mi>k</mi></math></span> vertices for <span><math><mrow><mn>2</mn><mo>≤</mo><mi>k</mi><mo>≤</mo><mn>5</mn></mrow></math></span>. Moreover, we develop a new graph transformation preserving the number of vertices, so that the resulting graph has a monotone behavior with respect to the number of short paths.</p></div>","PeriodicalId":50571,"journal":{"name":"Discrete Optimization","volume":null,"pages":null},"PeriodicalIF":1.1,"publicationDate":"2023-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"91729833","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Hard problems on box-totally dual integral polyhedra","authors":"Patrick Chervet ,&nbsp;Roland Grappe ,&nbsp;Mathieu Lacroix ,&nbsp;Francesco Pisanu ,&nbsp;Roberto Wolfler Calvo","doi":"10.1016/j.disopt.2023.100810","DOIUrl":"https://doi.org/10.1016/j.disopt.2023.100810","url":null,"abstract":"<div><p>In this paper, we study the complexity of some fundamental questions regarding box-totally dual integral (box-TDI) polyhedra. First, although box-TDI polyhedra have strong integrality properties, we prove that Integer Programming over box-TDI polyhedra is NP-complete, that is, finding an integer point optimizing a linear function over a box-TDI polyhedron is hard. Second, we complement the result of Ding et al. (2008) who proved that deciding whether a given system is box-TDI is co-NP-complete: we prove that recognizing whether a polyhedron is box-TDI is co-NP-complete.</p><p>To derive these complexity results, we exhibit new classes of totally equimodular matrices – a generalization of totally unimodular matrices – by characterizing the total equimodularity of incidence matrices of graphs.</p></div>","PeriodicalId":50571,"journal":{"name":"Discrete Optimization","volume":null,"pages":null},"PeriodicalIF":1.1,"publicationDate":"2023-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"92046424","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Optimal length cutting plane refutations of integer programs","authors":"K. Subramani,&nbsp;Piotr Wojciechowski","doi":"10.1016/j.disopt.2023.100806","DOIUrl":"https://doi.org/10.1016/j.disopt.2023.100806","url":null,"abstract":"<div><p><span>In this paper, we discuss the computational complexities of determining optimal length refutations of infeasible integer programs (IPs). We focus on three different types of refutations, namely read-once refutations, tree-like refutations, and dag-like refutations. For each refutation type, we are interested in finding the length of the shortest possible refutation of that type. In the case of this paper, the length of a refutation is equal to the number of inferences in that refutation. The refutations in this paper are also defined by the types of inferences that can be used to derive new constraints. We are interested in refutations with two inference rules. The first rule corresponds to the summation of two constraints and is called the ADD rule. The second rule is the DIV rule which divides a constraint by a positive integer. For integer programs, we study the complexity of approximating the length of the shortest refutation of each type (read-once, tree-like, and dag-like). In this paper, we show that the problem of finding the shortest read-once refutation is </span><strong>NPO PB-complete</strong>. Additionally, we show that the problem of finding the shortest tree-like refutation is <strong>NPO-hard</strong> for IPs. We also show that the problem of finding the shortest dag-like refutation is <strong>NPO-hard</strong> for IPs. Finally, we show that the problems of finding the shortest tree-like and dag-like refutations are in <strong>FPSPACE</strong>.</p></div>","PeriodicalId":50571,"journal":{"name":"Discrete Optimization","volume":null,"pages":null},"PeriodicalIF":1.1,"publicationDate":"2023-10-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49712009","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"On cut polytopes and graph minors","authors":"Konstantinos Kaparis ,&nbsp;Adam N. Letchford ,&nbsp;Ioannis Mourtos","doi":"10.1016/j.disopt.2023.100807","DOIUrl":"https://doi.org/10.1016/j.disopt.2023.100807","url":null,"abstract":"<div><p>The <em>max-cut problem</em> is a fundamental and much-studied <span><math><mi>NP</mi></math></span><span>-hard combinatorial optimisation problem<span>, with a wide range of applications. Several authors have shown that the max-cut problem can be solved in polynomial time if the underlying graph is free of certain </span></span><em>minors</em><span>. We give a polyhedral counterpart of these results. In particular, we show that, if a family of valid inequalities for the cut polytope satisfies certain conditions, then there is an associated minor-closed family of graphs on which the max-cut problem can be solved efficiently.</span></p></div>","PeriodicalId":50571,"journal":{"name":"Discrete Optimization","volume":null,"pages":null},"PeriodicalIF":1.1,"publicationDate":"2023-10-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49734196","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"On the general Z-type index of connected graphs","authors":"Chaohui Chen ,&nbsp;Wenshui Lin","doi":"10.1016/j.disopt.2023.100808","DOIUrl":"https://doi.org/10.1016/j.disopt.2023.100808","url":null,"abstract":"<div><p>Let <span><math><mrow><mi>G</mi><mo>=</mo><mrow><mo>(</mo><mi>V</mi><mo>,</mo><mi>E</mi><mo>)</mo></mrow></mrow></math></span><span> be a connected graph, and </span><span><math><mrow><mi>d</mi><mrow><mo>(</mo><mi>u</mi><mo>)</mo></mrow></mrow></math></span> the degree of vertex <span><math><mrow><mi>u</mi><mo>∈</mo><mi>V</mi></mrow></math></span>. We define the general <span><math><mi>Z</mi></math></span>-type index of <span><math><mi>G</mi></math></span> as <span><math><mrow><msub><mrow><mi>Z</mi></mrow><mrow><mi>α</mi><mo>,</mo><mi>β</mi></mrow></msub><mrow><mo>(</mo><mi>G</mi><mo>)</mo></mrow><mo>=</mo><msub><mrow><mo>∑</mo></mrow><mrow><mi>u</mi><mi>v</mi><mo>∈</mo><mi>E</mi></mrow></msub><msup><mrow><mrow><mo>[</mo><mi>d</mi><mrow><mo>(</mo><mi>u</mi><mo>)</mo></mrow><mo>+</mo><mi>d</mi><mrow><mo>(</mo><mi>v</mi><mo>)</mo></mrow><mo>−</mo><mi>β</mi><mo>]</mo></mrow></mrow><mrow><mi>α</mi></mrow></msup></mrow></math></span>, where <span><math><mi>α</mi></math></span> and <span><math><mi>β</mi></math></span><span> are two real numbers. This generalizes several famous topological indices, such as the first and second Zagreb indices, the general sum-connectivity index, the reformulated first Zagreb index, and the general Platt index, which have successful applications in QSPR/QSAR research. Hence, we are able to study these indices in a unified approach.</span></p><p>Let <span><math><mrow><mi>C</mi><mrow><mo>(</mo><mi>π</mi><mo>)</mo></mrow></mrow></math></span> the set of connected graphs with degree sequence <span><math><mi>π</mi></math></span>. In the present paper, under different conditions of <span><math><mi>α</mi></math></span> and <span><math><mi>β</mi></math></span>, we show that:</p><p><span><math><mrow><mo>(</mo><mn>1</mn><mo>)</mo></mrow></math></span><span> There exists a so-called BFS-graph having extremal </span><span><math><msub><mrow><mi>Z</mi></mrow><mrow><mi>α</mi><mo>,</mo><mi>β</mi></mrow></msub></math></span> index in <span><math><mrow><mi>C</mi><mrow><mo>(</mo><mi>π</mi><mo>)</mo></mrow></mrow></math></span>;</p><p><span><math><mrow><mo>(</mo><mn>2</mn><mo>)</mo></mrow></math></span> If <span><math><mi>π</mi></math></span> is the degree sequence of a tree, a unicyclic graph, or a bicyclic graph, with minimum degree 1, then there exists a special BFS-graph with extremal <span><math><msub><mrow><mi>Z</mi></mrow><mrow><mi>α</mi><mo>,</mo><mi>β</mi></mrow></msub></math></span> index in <span><math><mrow><mi>C</mi><mrow><mo>(</mo><mi>π</mi><mo>)</mo></mrow></mrow></math></span>;</p><p><span><math><mrow><mo>(</mo><mn>3</mn><mo>)</mo></mrow></math></span><span> The so-called majorization theorem of </span><span><math><msub><mrow><mi>Z</mi></mrow><mrow><mi>α</mi><mo>,</mo><mi>β</mi></mrow></msub></math></span> holds for trees, unicyclic graphs, and bicyclic graphs.</p><p>As applications of the above results, we determine the extremal graphs with maximum <span><math><msub><mrow><mi>Z</mi></mrow><mrow><mi>α</mi><mo>,</mo><m","PeriodicalId":50571,"journal":{"name":"Discrete Optimization","volume":null,"pages":null},"PeriodicalIF":1.1,"publicationDate":"2023-10-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49712365","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The k-aggregation closure for covering sets","authors":"Haoran Zhu","doi":"10.1016/j.disopt.2023.100805","DOIUrl":"https://doi.org/10.1016/j.disopt.2023.100805","url":null,"abstract":"<div><p>In this paper, we will answer a more general version of one of the questions proposed by Bodur et al. (2017). Specifically, we show that the <span><math><mi>k</mi></math></span><span>-aggregation closure of a covering set is a polyhedron.</span></p></div>","PeriodicalId":50571,"journal":{"name":"Discrete Optimization","volume":null,"pages":null},"PeriodicalIF":1.1,"publicationDate":"2023-09-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49712363","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Convexifying multilinear sets with cardinality constraints: Structural properties, nested case and extensions","authors":"Rui Chen ,&nbsp;Sanjeeb Dash ,&nbsp;Oktay Günlük","doi":"10.1016/j.disopt.2023.100804","DOIUrl":"https://doi.org/10.1016/j.disopt.2023.100804","url":null,"abstract":"<div><p><span>The problem of minimizing a multilinear function of binary variables is a well-studied NP-hard problem. The set of solutions of the standard linearization of this problem is called the multilinear set. We study a cardinality constrained version of it with upper and lower bounds on the number of nonzero variables. We call the set of solutions of the standard linearization of this problem a multilinear set with cardinality constraints. We characterize a set of conditions on these multilinear terms (called </span><em>properness</em><span>) and observe that under these conditions the convex hull<span> description of the set is tractable via an extended formulation. We then give an explicit polyhedral description of the convex hull when the multilinear terms have a nested structure. Our description has an exponential number of inequalities which can be separated in polynomial time. Finally, we generalize these inequalities to obtain valid inequalities for the general case.</span></span></p></div>","PeriodicalId":50571,"journal":{"name":"Discrete Optimization","volume":null,"pages":null},"PeriodicalIF":1.1,"publicationDate":"2023-09-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49733924","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"More on online weighted edge coloring","authors":"Leah Epstein","doi":"10.1016/j.disopt.2023.100803","DOIUrl":"https://doi.org/10.1016/j.disopt.2023.100803","url":null,"abstract":"<div><p><span><span>We revisit online weighted edge coloring. In this problem, weighted edges of a graph are presented one by one, to be colored with positive integers. It is required that for every vertex, all its edges of every common color will have a total weight not exceeding 1. We provide an improved upper bound on the performance of a </span>greedy algorithm First Fit for the case of arbitrary weights, and for the case of weights not exceeding </span><span><math><mfrac><mrow><mn>1</mn></mrow><mrow><mn>2</mn></mrow></mfrac></math></span>. Here, the meaning of First Fit is that every edge is colored with a color of the smallest index that will keep the coloring valid. This improves the state-of-the-art with respect to online algorithms for this variant of edge coloring. We also show new lower bounds on the performance of any online algorithm with weights in <span><math><mrow><mo>(</mo><mn>0</mn><mo>,</mo><mfrac><mrow><mn>1</mn></mrow><mrow><mi>t</mi></mrow></mfrac><mo>]</mo></mrow></math></span>, for any integer <span><math><mrow><mi>t</mi><mo>≥</mo><mn>2</mn></mrow></math></span>.</p></div>","PeriodicalId":50571,"journal":{"name":"Discrete Optimization","volume":null,"pages":null},"PeriodicalIF":1.1,"publicationDate":"2023-09-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49733922","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Constructing extremal triangle-free graphs using integer programming","authors":"Ali Erdem Banak,&nbsp;Tınaz Ekim,&nbsp;Z. Caner Taşkın","doi":"10.1016/j.disopt.2023.100802","DOIUrl":"https://doi.org/10.1016/j.disopt.2023.100802","url":null,"abstract":"<div><p><span>The maximum number of edges in a graph with matching number </span><span><math><mi>m</mi></math></span><span> and maximum degree </span><span><math><mi>d</mi></math></span><span> has been determined in Chvátal and Hanson (1976) and Balachandran and Khare (2009), where some extremal graphs have also been provided. Then, a new question has emerged: how the maximum edge count is affected by forbidding some subgraphs occurring in these extremal graphs? In Ahanjideh et al. (2022), the problem is solved in triangle-free graphs for </span><span><math><mrow><mi>d</mi><mo>≥</mo><mi>m</mi></mrow></math></span>, and for <span><math><mrow><mi>d</mi><mo>&lt;</mo><mi>m</mi></mrow></math></span> with either <span><math><mrow><mi>Z</mi><mrow><mo>(</mo><mi>d</mi><mo>)</mo></mrow><mo>≤</mo><mi>m</mi><mo>&lt;</mo><mn>2</mn><mi>d</mi></mrow></math></span> or <span><math><mrow><mi>d</mi><mo>≤</mo><mn>6</mn></mrow></math></span>, where <span><math><mrow><mi>Z</mi><mrow><mo>(</mo><mi>d</mi><mo>)</mo></mrow></mrow></math></span> is approximately <span><math><mrow><mn>5</mn><mi>d</mi><mo>/</mo><mn>4</mn></mrow></math></span><span>. The authors derived structural properties of triangle-free extremal graphs, which allows us to focus on constructing small extremal components to form an extremal graph. Based on these findings, in this paper, we develop an integer programming formulation for constructing extremal graphs. Since our formulation is highly symmetric, we use our own implementation of Orbital Branching to reduce symmetry. We also implement our integer programming formulation so that the feasible region is restricted iteratively. Using a combination of the two approaches, we expand the solution into </span><span><math><mrow><mi>d</mi><mo>≤</mo><mn>10</mn></mrow></math></span> instead of <span><math><mrow><mi>d</mi><mo>≤</mo><mn>6</mn></mrow></math></span> for <span><math><mrow><mi>m</mi><mo>&gt;</mo><mi>d</mi></mrow></math></span>. Our results endorse the formula for the number of edges in all extremal triangle-free graphs conjectured in Ahanjideh et al. (2022).</p></div>","PeriodicalId":50571,"journal":{"name":"Discrete Optimization","volume":null,"pages":null},"PeriodicalIF":1.1,"publicationDate":"2023-09-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49733923","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}