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  Subjects -> MATHEMATICS (Total: 894 journals)
    - APPLIED MATHEMATICS (74 journals)
    - GEOMETRY AND TOPOLOGY (20 journals)
    - MATHEMATICS (662 journals)
    - MATHEMATICS (GENERAL) (42 journals)
    - NUMERICAL ANALYSIS (19 journals)
    - PROBABILITIES AND MATH STATISTICS (77 journals)

MATHEMATICS (662 journals)                  1 2 3 4 | Last

Showing 1 - 200 of 538 Journals sorted alphabetically
Abakós     Open Access   (Followers: 4)
Abhandlungen aus dem Mathematischen Seminar der Universitat Hamburg     Hybrid Journal   (Followers: 3)
Academic Voices : A Multidisciplinary Journal     Open Access   (Followers: 2)
Accounting Perspectives     Full-text available via subscription   (Followers: 7)
ACM Transactions on Algorithms (TALG)     Hybrid Journal   (Followers: 16)
ACM Transactions on Computational Logic (TOCL)     Hybrid Journal   (Followers: 4)
ACM Transactions on Mathematical Software (TOMS)     Hybrid Journal   (Followers: 6)
ACS Applied Materials & Interfaces     Full-text available via subscription   (Followers: 25)
Acta Applicandae Mathematicae     Hybrid Journal   (Followers: 1)
Acta Mathematica     Hybrid Journal   (Followers: 11)
Acta Mathematica Hungarica     Hybrid Journal   (Followers: 2)
Acta Mathematica Scientia     Full-text available via subscription   (Followers: 5)
Acta Mathematica Sinica, English Series     Hybrid Journal   (Followers: 6)
Acta Mathematica Vietnamica     Hybrid Journal  
Acta Mathematicae Applicatae Sinica, English Series     Hybrid Journal  
Advanced Science Letters     Full-text available via subscription   (Followers: 9)
Advances in Applied Clifford Algebras     Hybrid Journal   (Followers: 3)
Advances in Calculus of Variations     Hybrid Journal   (Followers: 2)
Advances in Catalysis     Full-text available via subscription   (Followers: 5)
Advances in Complex Systems     Hybrid Journal   (Followers: 7)
Advances in Computational Mathematics     Hybrid Journal   (Followers: 15)
Advances in Decision Sciences     Open Access   (Followers: 5)
Advances in Difference Equations     Open Access   (Followers: 2)
Advances in Fixed Point Theory     Open Access   (Followers: 5)
Advances in Geosciences (ADGEO)     Open Access   (Followers: 11)
Advances in Linear Algebra & Matrix Theory     Open Access   (Followers: 2)
Advances in Materials Sciences     Open Access   (Followers: 16)
Advances in Mathematical Physics     Open Access   (Followers: 5)
Advances in Mathematics     Full-text available via subscription   (Followers: 10)
Advances in Numerical Analysis     Open Access   (Followers: 4)
Advances in Operations Research     Open Access   (Followers: 11)
Advances in Porous Media     Full-text available via subscription   (Followers: 4)
Advances in Pure and Applied Mathematics     Hybrid Journal   (Followers: 6)
Advances in Pure Mathematics     Open Access   (Followers: 4)
Advances in Science and Research (ASR)     Open Access   (Followers: 6)
Aequationes Mathematicae     Hybrid Journal   (Followers: 2)
African Journal of Educational Studies in Mathematics and Sciences     Full-text available via subscription   (Followers: 5)
African Journal of Mathematics and Computer Science Research     Open Access   (Followers: 4)
Afrika Matematika     Hybrid Journal   (Followers: 1)
Air, Soil & Water Research     Open Access   (Followers: 9)
AKSIOMA Journal of Mathematics Education     Open Access   (Followers: 1)
Al-Jabar : Jurnal Pendidikan Matematika     Open Access  
Algebra and Logic     Hybrid Journal   (Followers: 4)
Algebra Colloquium     Hybrid Journal   (Followers: 4)
Algebra Universalis     Hybrid Journal   (Followers: 2)
Algorithmic Operations Research     Full-text available via subscription   (Followers: 5)
Algorithms     Open Access   (Followers: 11)
Algorithms Research     Open Access   (Followers: 1)
American Journal of Biostatistics     Open Access   (Followers: 9)
American Journal of Computational and Applied Mathematics     Open Access   (Followers: 4)
American Journal of Mathematical Analysis     Open Access  
American Journal of Mathematics     Full-text available via subscription   (Followers: 7)
American Journal of Operations Research     Open Access   (Followers: 5)
American Mathematical Monthly     Full-text available via subscription   (Followers: 6)
An International Journal of Optimization and Control: Theories & Applications     Open Access   (Followers: 7)
Analele Universitatii Ovidius Constanta - Seria Matematica     Open Access   (Followers: 1)
Analysis     Hybrid Journal   (Followers: 2)
Analysis and Applications     Hybrid Journal   (Followers: 1)
Analysis and Mathematical Physics     Hybrid Journal   (Followers: 3)
Analysis Mathematica     Full-text available via subscription  
Annales Mathematicae Silesianae     Open Access  
Annales mathématiques du Québec     Hybrid Journal   (Followers: 4)
Annales UMCS, Mathematica     Open Access   (Followers: 1)
Annales Universitatis Paedagogicae Cracoviensis. Studia Mathematica     Open Access  
Annali di Matematica Pura ed Applicata     Hybrid Journal   (Followers: 1)
Annals of Combinatorics     Hybrid Journal   (Followers: 3)
Annals of Data Science     Hybrid Journal   (Followers: 11)
Annals of Discrete Mathematics     Full-text available via subscription   (Followers: 6)
Annals of Mathematics     Full-text available via subscription  
Annals of Mathematics and Artificial Intelligence     Hybrid Journal   (Followers: 7)
Annals of Pure and Applied Logic     Open Access   (Followers: 2)
Annals of the Alexandru Ioan Cuza University - Mathematics     Open Access  
Annals of the Institute of Statistical Mathematics     Hybrid Journal   (Followers: 1)
Annals of West University of Timisoara - Mathematics     Open Access  
Annuaire du Collège de France     Open Access   (Followers: 5)
Applicable Algebra in Engineering, Communication and Computing     Hybrid Journal   (Followers: 2)
Applications of Mathematics     Hybrid Journal   (Followers: 1)
Applied Categorical Structures     Hybrid Journal   (Followers: 2)
Applied Computational Intelligence and Soft Computing     Open Access   (Followers: 12)
Applied Mathematics     Open Access   (Followers: 3)
Applied Mathematics     Open Access   (Followers: 4)
Applied Mathematics & Optimization     Hybrid Journal   (Followers: 4)
Applied Mathematics - A Journal of Chinese Universities     Hybrid Journal  
Applied Mathematics Letters     Full-text available via subscription   (Followers: 1)
Applied Mathematics Research eXpress     Hybrid Journal   (Followers: 1)
Applied Network Science     Open Access   (Followers: 1)
Applied Numerical Mathematics     Hybrid Journal   (Followers: 5)
Applied Spatial Analysis and Policy     Hybrid Journal   (Followers: 4)
Arab Journal of Mathematical Sciences     Open Access   (Followers: 3)
Arabian Journal of Mathematics     Open Access   (Followers: 2)
Archive for Mathematical Logic     Hybrid Journal   (Followers: 1)
Archive of Applied Mechanics     Hybrid Journal   (Followers: 5)
Archive of Numerical Software     Open Access  
Archives of Computational Methods in Engineering     Hybrid Journal   (Followers: 4)
Arkiv för Matematik     Hybrid Journal   (Followers: 1)
Arnold Mathematical Journal     Hybrid Journal   (Followers: 1)
Artificial Satellites : The Journal of Space Research Centre of Polish Academy of Sciences     Open Access   (Followers: 20)
Asia-Pacific Journal of Operational Research     Hybrid Journal   (Followers: 3)
Asian Journal of Algebra     Open Access   (Followers: 1)
Asian Journal of Current Engineering & Maths     Open Access  
Asian-European Journal of Mathematics     Hybrid Journal   (Followers: 2)
Australian Mathematics Teacher, The     Full-text available via subscription   (Followers: 7)
Australian Primary Mathematics Classroom     Full-text available via subscription   (Followers: 3)
Australian Senior Mathematics Journal     Full-text available via subscription   (Followers: 1)
Automatic Documentation and Mathematical Linguistics     Hybrid Journal   (Followers: 5)
Axioms     Open Access  
Baltic International Yearbook of Cognition, Logic and Communication     Open Access  
Basin Research     Hybrid Journal   (Followers: 5)
BIBECHANA     Open Access   (Followers: 2)
BIT Numerical Mathematics     Hybrid Journal  
BoEM - Boletim online de Educação Matemática     Open Access  
Boletim Cearense de Educação e História da Matemática     Open Access  
Boletim de Educação Matemática     Open Access  
Boletín de la Sociedad Matemática Mexicana     Hybrid Journal  
Bollettino dell'Unione Matematica Italiana     Full-text available via subscription   (Followers: 1)
British Journal of Mathematical and Statistical Psychology     Full-text available via subscription   (Followers: 21)
Bruno Pini Mathematical Analysis Seminar     Open Access  
Buletinul Academiei de Stiinte a Republicii Moldova. Matematica     Open Access   (Followers: 9)
Bulletin des Sciences Mathamatiques     Full-text available via subscription   (Followers: 4)
Bulletin of Dnipropetrovsk University. Series : Communications in Mathematical Modeling and Differential Equations Theory     Open Access   (Followers: 1)
Bulletin of Mathematical Sciences     Open Access   (Followers: 1)
Bulletin of the Brazilian Mathematical Society, New Series     Hybrid Journal  
Bulletin of the London Mathematical Society     Hybrid Journal   (Followers: 3)
Bulletin of the Malaysian Mathematical Sciences Society     Hybrid Journal  
Calculus of Variations and Partial Differential Equations     Hybrid Journal  
Canadian Journal of Science, Mathematics and Technology Education     Hybrid Journal   (Followers: 20)
Carpathian Mathematical Publications     Open Access   (Followers: 1)
Catalysis in Industry     Hybrid Journal   (Followers: 1)
CEAS Space Journal     Hybrid Journal   (Followers: 1)
CHANCE     Hybrid Journal   (Followers: 5)
Chaos, Solitons & Fractals     Hybrid Journal   (Followers: 3)
ChemSusChem     Hybrid Journal   (Followers: 7)
Chinese Annals of Mathematics, Series B     Hybrid Journal  
Chinese Journal of Catalysis     Full-text available via subscription   (Followers: 2)
Chinese Journal of Mathematics     Open Access  
Clean Air Journal     Full-text available via subscription   (Followers: 2)
Cogent Mathematics     Open Access   (Followers: 2)
Cognitive Computation     Hybrid Journal   (Followers: 4)
Collectanea Mathematica     Hybrid Journal  
College Mathematics Journal     Full-text available via subscription   (Followers: 3)
COMBINATORICA     Hybrid Journal  
Combustion Theory and Modelling     Hybrid Journal   (Followers: 13)
Commentarii Mathematici Helvetici     Hybrid Journal   (Followers: 1)
Communications in Contemporary Mathematics     Hybrid Journal  
Communications in Mathematical Physics     Hybrid Journal   (Followers: 1)
Communications On Pure & Applied Mathematics     Hybrid Journal   (Followers: 3)
Complex Analysis and its Synergies     Open Access   (Followers: 2)
Complex Variables and Elliptic Equations: An International Journal     Hybrid Journal  
Complexus     Full-text available via subscription  
Composite Materials Series     Full-text available via subscription   (Followers: 9)
Comptes Rendus Mathematique     Full-text available via subscription   (Followers: 1)
Computational and Applied Mathematics     Hybrid Journal   (Followers: 2)
Computational and Mathematical Methods in Medicine     Open Access   (Followers: 2)
Computational and Mathematical Organization Theory     Hybrid Journal   (Followers: 2)
Computational Complexity     Hybrid Journal   (Followers: 4)
Computational Mathematics and Modeling     Hybrid Journal   (Followers: 8)
Computational Mechanics     Hybrid Journal   (Followers: 4)
Computational Methods and Function Theory     Hybrid Journal  
Computational Optimization and Applications     Hybrid Journal   (Followers: 7)
Computers & Mathematics with Applications     Full-text available via subscription   (Followers: 6)
Concrete Operators     Open Access   (Followers: 4)
Confluentes Mathematici     Hybrid Journal  
COSMOS     Hybrid Journal  
Cryptography and Communications     Hybrid Journal   (Followers: 14)
Cuadernos de Investigación y Formación en Educación Matemática     Open Access  
Cubo. A Mathematical Journal     Open Access  
Czechoslovak Mathematical Journal     Hybrid Journal   (Followers: 1)
Demographic Research     Open Access   (Followers: 11)
Demonstratio Mathematica     Open Access  
Dependence Modeling     Open Access  
Design Journal : An International Journal for All Aspects of Design     Hybrid Journal   (Followers: 28)
Developments in Clay Science     Full-text available via subscription   (Followers: 1)
Developments in Mineral Processing     Full-text available via subscription   (Followers: 3)
Dhaka University Journal of Science     Open Access  
Differential Equations and Dynamical Systems     Hybrid Journal   (Followers: 3)
Discrete Mathematics     Hybrid Journal   (Followers: 8)
Discrete Mathematics & Theoretical Computer Science     Open Access  
Discrete Mathematics, Algorithms and Applications     Hybrid Journal   (Followers: 2)
Discussiones Mathematicae Graph Theory     Open Access   (Followers: 1)
Dnipropetrovsk University Mathematics Bulletin     Open Access  
Doklady Mathematics     Hybrid Journal  
Duke Mathematical Journal     Full-text available via subscription   (Followers: 1)
Eco Matemático     Open Access  
Edited Series on Advances in Nonlinear Science and Complexity     Full-text available via subscription  
Electronic Journal of Differential Equations     Open Access  
Electronic Journal of Graph Theory and Applications     Open Access   (Followers: 2)
Electronic Notes in Discrete Mathematics     Full-text available via subscription   (Followers: 2)
Elemente der Mathematik     Full-text available via subscription   (Followers: 3)
Energy for Sustainable Development     Hybrid Journal   (Followers: 9)
Enseñanza de las Ciencias : Revista de Investigación y Experiencias Didácticas     Open Access  
Ensino da Matemática em Debate     Open Access  
Entropy     Open Access   (Followers: 5)
ESAIM: Control Optimisation and Calculus of Variations     Full-text available via subscription   (Followers: 1)
European Journal of Combinatorics     Full-text available via subscription   (Followers: 5)
European Journal of Mathematics     Hybrid Journal   (Followers: 1)
European Scientific Journal     Open Access   (Followers: 2)
Experimental Mathematics     Hybrid Journal   (Followers: 4)
Expositiones Mathematicae     Hybrid Journal   (Followers: 2)
Facta Universitatis, Series : Mathematics and Informatics     Open Access  
Fasciculi Mathematici     Open Access  

        1 2 3 4 | Last

Journal Cover COMBINATORICA
  [SJR: 1.296]   [H-I: 38]   [0 followers]  Follow
    
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
   ISSN (Print) 1439-6912 - ISSN (Online) 0209-9683
   Published by Springer-Verlag Homepage  [2354 journals]
  • Fractional covers and matchings in families of weighted d -intervals
    • Authors: Ron Aharoni; Tomáš Kaiser; Shira Zerbib
      Pages: 555 - 572
      Abstract: A d-interval is a union of at most d disjoint closed intervals on a fixed line. Tardos [14] and the second author [11] used topological tools to bound the transversal number τ of a family H of d-intervals in terms of d and the matching number ν of H. We investigate the weighted and fractional versions of this problem and prove upper bounds that are tight up to constant factors. We apply both a topological method and an approach of Alon [1]. For the use of the latter, we prove a weighted version of Turán’s theorem. We also provide proofs of the upper bounds of [11] that are more direct than the original proofs.
      PubDate: 2017-08-01
      DOI: 10.1007/s00493-016-3174-7
      Issue No: Vol. 37, No. 4 (2017)
       
  • Powers of Hamilton cycles in pseudorandom graphs
    • Authors: Peter Allen; Julia Böttcher; Hiệp Hàn; Yoshiharu Kohayakawa; Yury Person
      Pages: 573 - 616
      Abstract: We study the appearance of powers of Hamilton cycles in pseudorandom graphs, using the following comparatively weak pseudorandomness notion. A graph G is (ε,p,k,ℓ)-pseudorandom if for all disjoint X and Y ⊂ V(G) with X ≥εp k n and Y ≥εp ℓ n we have e(X,Y)=(1±ε)p X Y . We prove that for all β>0 there is an ε>0 such that an (ε,p,1,2)-pseudorandom graph on n vertices with minimum degree at least βpn contains the square of a Hamilton cycle. In particular, this implies that (n,d,λ)-graphs with λ≪d 5/2 n -3/2 contain the square of a Hamilton cycle, and thus a triangle factor if n is a multiple of 3. This improves on a result of Krivelevich, Sudakov and Szabó [27]. We also extend our result to higher powers of Hamilton cycles and establish corresponding counting versions.
      PubDate: 2017-08-01
      DOI: 10.1007/s00493-015-3228-2
      Issue No: Vol. 37, No. 4 (2017)
       
  • The typical structure of graphs with no large cliques
    • Authors: József Balogh; Neal Bushaw; Maurício Collares; Hong Liu; Robert Morris; Maryam Sharifzadeh
      Pages: 617 - 632
      Abstract: In 1987, Kolaitis, Prömel and Rothschild proved that, for every fixed r∈ℕ, almost every n-vertex K r+1-free graph is r-partite. In this paper we extend this result to all functions r = r(n) with r ⩽ (logn)1/4. The proof combines a new (close to sharp) supersaturation version of the Erdős-Simonovits stability theorem, the hypergraph container method, and a counting technique developed by Balogh, Bollobás and Simonovits.
      PubDate: 2017-08-01
      DOI: 10.1007/s00493-015-3290-9
      Issue No: Vol. 37, No. 4 (2017)
       
  • Computing the partition function for graph homomorphisms
    • Authors: Alexander Barvinok; Pablo Soberón
      Pages: 633 - 650
      Abstract: We introduce the partition function of edge-colored graph homomorphisms, of which the usual partition function of graph homomorphisms is a specialization, and present an efficient algorithm to approximate it in a certain domain. Corollaries include effcient algorithms for computing weighted sums approximating the number of k-colorings and the number of independent sets in a graph, as well as an effcient procedure to distinguish pairs of edge-colored graphs with many color-preserving homomorphisms G → H from pairs of graphs that need to be substantially modified to acquire a color-preserving homomorphism G → H.
      PubDate: 2017-08-01
      DOI: 10.1007/s00493-016-3357-2
      Issue No: Vol. 37, No. 4 (2017)
       
  • Regular families of forests, antichains and duality pairs of relational
           structures
    • Authors: Péter L. Erdős; Dömötör Pálvölgyi; Claude Tardif; Gábor Tardos
      Pages: 651 - 672
      Abstract: Homomorphism duality pairs play a crucial role in the theory of relational structures and in the Constraint Satisfaction Problem. The case where both classes are finite is fully characterized. The case when both sides are infinite seems to be very complex. It is also known that no finite-infinite duality pair is possible if we make the additional restriction that both classes are antichains. In this paper we characterize the infinite-finite antichain dualities and infinite-finite dualities with trees or forests on the left hand side. This work builds on our earlier papers [6] that gave several examples of infinite-finite antichain duality pairs of directed graphs and [7] giving a complete characterization for caterpillar dualities.
      PubDate: 2017-08-01
      DOI: 10.1007/s00493-015-3003-4
      Issue No: Vol. 37, No. 4 (2017)
       
  • Generalising Fisher’s inequality to coverings and packings
    • Authors: Daniel Horsley
      Pages: 673 - 696
      Abstract: In 1940 Fisher famously showed that if there exists a non-trivial (v,k,λ)-design, then λ(v-1)⩾k(k-1). Subsequently Bose gave an elegant alternative proof of Fisher’s result. Here, we show that the idea behind Bose’s proof can be generalised to obtain new bounds on the number of blocks in (v,k,λ)-coverings and -packings with λ(v-1)<k(k-1).
      PubDate: 2017-08-01
      DOI: 10.1007/s00493-016-3326-9
      Issue No: Vol. 37, No. 4 (2017)
       
  • Compatible Hamilton cycles in Dirac graphs
    • Authors: Michael Krivelevich; Choongbum Lee; Benny Sudakov
      Pages: 697 - 732
      Abstract: A graph is Hamiltonian if it contains a cycle passing through every vertex exactly once. A celebrated theorem of Dirac from 1952 asserts that every graph on n≥3 vertices with minimum degree at least n/2 is Hamiltonian. We refer to such graphs as Dirac graphs. In this paper we obtain the following strengthening of this result. Given a graph G=(V,E), an incompatibility system F over G is a family F = {F v } v∈V such that for every v∈V, the set F v is a family of unordered pairs F v ⊆ {{e,e′}}: e ≠ e′ ∈ E,e ∩ e′ = {v}}. An incompatibility system is Δ-bounded if for every vertex v and an edge e incident to v, there are at most Δ pairs in F v containing e. We say that a cycle C in G is compatible with F if every pair of incident edges e,e′ of C satisfies {e,e′}∉F v , where v=e ∩ e′. This notion is partly motivated by a concept of transition systems defined by Kotzig in 1968, and can be viewed as a quantitative measure of robustness of graph properties. We prove that there is a constant μ>0 such that for every μn-bounded incompatibility system F over a Dirac graph G, there exists a Hamilton cycle compatible with F. This settles in a very strong form a conjecture of Häggkvist from 1988.
      PubDate: 2017-08-01
      DOI: 10.1007/s00493-016-3328-7
      Issue No: Vol. 37, No. 4 (2017)
       
  • Lifts, derandomization, and diameters of Schreier graphs of Mealy automata
    • Authors: Anton Malyshev; Igor Pak
      Pages: 733 - 765
      Abstract: It is known that random 2-lifts of graphs give rise to expander graphs. We present a new conjectured derandomization of this construction based on certain Mealy automata. We verify that these graphs have polylogarithmic diameter, and present a class of automata for which the same is true. However, we also show that some automata in this class do not give rise to expander graphs.
      PubDate: 2017-08-01
      DOI: 10.1007/s00493-016-3306-0
      Issue No: Vol. 37, No. 4 (2017)
       
  • An exponential-type upper bound for Folkman numbers
    • Authors: Vojtěch Rödl; Andrzej Ruciński; Mathias Schacht
      Pages: 767 - 784
      Abstract: For given integers k and r, the Folkman number f(k;r) is the smallest number of vertices in a graph G which contains no clique on k+1 vertices, yet for every partition of its edges into r parts, some part contains a clique of order k. The existence (finiteness) of Folkman numbers was established by Folkman (1970) for r=2 and by Nešetřil and Rödl (1976) for arbitrary r, but these proofs led to very weak upper bounds on f(k;r). Recently, Conlon and Gowers and independently the authors obtained a doubly exponential bound on f(k;2). Here, we establish a further improvement by showing an upper bound on f(k;r) which is exponential in a polynomial of k and r. This is comparable to the known lower bound 2 Ω(rk). Our proof relies on a recent result of Saxton and Thomason (or, alternatively, on a recent result of Balogh, Morris, and Samotij) from which we deduce a quantitative version of Ramsey’s theorem in random graphs.
      PubDate: 2017-08-01
      DOI: 10.1007/s00493-015-3298-1
      Issue No: Vol. 37, No. 4 (2017)
       
  • Infinitely connected subgraphs in graphs of uncountable chromatic number
    • Authors: Carsten Thomassen
      Pages: 785 - 793
      Abstract: Erdős and Hajnal conjectured in 1966 that every graph of uncountable chromatic number contains a subgraph of infinite connectivity. We prove that every graph of uncountable chromatic number has a subgraph which has uncountable chromatic number and infinite edge-connectivity. We also prove that, if each orientation of a graph G has a vertex of infinite outdegree, then G contains an uncountable subgraph of infinite edge-connectivity.
      PubDate: 2017-08-01
      DOI: 10.1007/s00493-016-3436-4
      Issue No: Vol. 37, No. 4 (2017)
       
  • Minimal normal graph covers
    • Authors: David Gajser; Bojan Mohar
      Abstract: A graph is normal if it admits a clique cover C and a stable set cover S such that each clique in C and each stable set in S have a vertex in common. The pair (C,S) is a normal cover of the graph. We present the following extremal property of normal covers. For positive integers c, s, if a graph with n vertices admits a normal cover with cliques of sizes at most c and stable sets of sizes at most s, then c+s≥log2(n). For infinitely many n, we also give a construction of a graph with n vertices that admits a normal cover with cliques and stable sets of sizes less than 0.87log2(n). Furthermore, we show that for all n, there exists a normal graph with n vertices, clique number Θ(log2(n)) and independence number Θ(log2(n)). When c or s are very small, we can describe all normal graphs with the largest possible number of vertices that allow a normal cover with cliques of sizes at most c and stable sets of sizes at most s. However, such extremal graphs remain elusive even for moderately small values of c and s.
      PubDate: 2017-08-14
      DOI: 10.1007/s00493-017-3559-2
       
  • Edge lower bounds for list critical graphs, via discharging
    • Authors: Daniel W. Cranston; Landon Rabern
      Abstract: A graph G is k-critical if G is not (k − 1)-colorable, but every proper subgraph of G is (k − 1)-colorable. A graph G is k-choosable if G has an L-coloring from every list assignment L with L(v) =k for all v, and a graph G is k-list-critical if G is not (k−1)-choosable, but every proper subgraph of G is (k−1)-choosable. The problem of determining the minimum number of edges in a k-critical graph with n vertices has been widely studied, starting with work of Gallai and culminating with the seminal results of Kostochka and Yancey, who essentially solved the problem. In this paper, we improve the best known lower bound on the number of edges in a k-list-critical graph. In fact, our result on k-list-critical graphs is derived from a lower bound on the number of edges in a graph with Alon–Tarsi number at least k. Our proof uses the discharging method, which makes it simpler and more modular than previous work in this area.
      PubDate: 2017-08-14
      DOI: 10.1007/s00493-016-3584-6
       
  • Count matroids of group-labeled graphs
    • Authors: Rintaro Ikeshita; Shin-ichi Tanigawa
      Abstract: A graph G = (V, E) is called (k, ℓ)-sparse if F ≤ k V (F) − ℓ for any nonempty F ⊆ E, where V (F) denotes the set of vertices incident to F. It is known that the family of the edge sets of (k, ℓ)-sparse subgraphs forms the family of independent sets of a matroid, called the (k, ℓ)-count matroid of G. In this paper we shall investigate lifts of the (k, ℓ)- count matroids by using group labelings on the edge set. By introducing a new notion called near-balancedness, we shall identify a new class of matroids whose independence condition is described as a count condition of the form F ≤ k V (F) −ℓ+α ψ (F) for some function α ψ determined by a given group labeling ψ on E.
      PubDate: 2017-08-14
      DOI: 10.1007/s00493-016-3469-8
       
  • Essential dimension and the flats spanned by a point set
    • Authors: Ben Lund
      Abstract: Let P be a finite set of points in ℝ d or ℂ d .We answer a question of Purdy on the conditions under which the number of hyperplanes spanned by P is at least the number of (d−2)-flats spanned by P. In answering this question, we define a new measure of the degeneracy of a point set with respect to affine subspaces, termed the essential dimension. We use the essential dimension to give an asymptotic expression for the number of k-flats spanned by P, for 1≤k≤d−1.
      PubDate: 2017-08-14
      DOI: 10.1007/s00493-016-3602-8
       
  • List supermodular coloring
    • Authors: Satoru Iwata; Yu Yokoi
      Abstract: In 1995, Galvin provided an elegant proof for the list edge coloring conjecture for bipartite graphs, utilizing the stable matching theorem of Gale and Shapley. In this paper, we generalize Galvin’s result to the setting of supermodular coloring, introduced by Schrijver, with the aid of the monochromatic path theorem of Sands, Sauer andWoodrow. Our result derives a list coloring version of Gupta’s theorem, which can also be proven directly from Galvin’s theorem.
      PubDate: 2017-08-14
      DOI: 10.1007/s00493-017-3670-4
       
  • Treewidth of grid subsets
    • Authors: Eli Berger; Zdenĕk Dvořák; Sergey Norin
      Abstract: Let Q n be the 3-dimensional n×n×n grid with all non-decreasing diagonals (including the facial ones) in its constituent unit cubes. Suppose that a set S ⊆ V (Q n ) separates the left side of the grid from the right side. We show that S induces a subgraph of tree-width at least \(\frac{n}{{\sqrt {18} }} = - 1\) . We use a generalization of this claim to prove that the vertex set of Q n cannot be partitioned to two parts, each of them inducing a subgraph of bounded tree-width.
      PubDate: 2017-08-14
      DOI: 10.1007/s00493-017-3548-5
       
  • Chromatic number of ordered graphs with forbidden ordered subgraphs
    • Authors: Maria Axenovich; Jonathan Rollin; Torsten Ueckerdt
      Abstract: It is well-known that the graphs not containing a given graph H as a subgraph have bounded chromatic number if and only if H is acyclic. Here we consider ordered graphs, i.e., graphs with a linear ordering ≺ on their vertex set, and the function $${f_ \prec }\left( H \right) = \sup \left\{ {\chi \left( G \right) G \in For{b_ \prec }\left( H \right)} \right\},$$ where Forb≺(H) denotes the set of all ordered graphs that do not contain a copy of H. If H contains a cycle, then as in the case of unordered graphs, f ≺(H)=∞. However, in contrast to the unordered graphs, we describe an infinite family of ordered forests H with f ≺(H) =∞. An ordered graph is crossing if there are two edges uv and u′v′ with u ≺ u′ ≺ v ≺ v′. For connected crossing ordered graphs H we reduce the problem of determining whether f ≺(H) ≠∞ to a family of so-called monotonically alternating trees. For non-crossing H we prove that f ≺(H) ≠∞ if and only if H is acyclic and does not contain a copy of any of the five special ordered forests on four or five vertices, which we call bonnets. For such forests H, we show that f ≺(H)⩽2 V(H) and that f ≺(H)⩽2 V (H) −3 if H is connected.
      PubDate: 2017-08-14
      DOI: 10.1007/s00493-017-3593-0
       
  • Topology of complexes of edge covering partite graphs and hypergraphs
    • Authors: Victor A. Vassiliev
      Abstract: We describe the homotopy types of complexes of partite graphs and hypergraphs with a fixed set of vertices covered by their edges.
      PubDate: 2017-08-14
      DOI: 10.1007/s00493-017-3508-0
       
  • Sparsity and dimension
    • Authors: Gwenaël Joret; Piotr Micek; Veit Wiechert
      Abstract: We prove that posets of bounded height whose cover graphs belong to a fixed class with bounded expansion have bounded dimension. Bounded expansion, introduced by Nešetřil and Ossona de Mendez as a model for sparsity in graphs, is a property that is naturally satisfied by a wide range of graph classes, from graph structure theory (graphs excluding a minor or a topological minor) to graph drawing (e.g. graphs with bounded book thickness). Therefore, our theorem generalizes a number of results including the most recent one for posets of bounded height with cover graphs excluding a fixed graph as a topological minor. We also show that the result is in a sense best possible, as it does not extend to nowhere dense classes; in fact, it already fails for cover graphs with locally bounded treewidth.
      PubDate: 2017-08-14
      DOI: 10.1007/s00493-017-3638-4
       
  • A proof of the block model threshold conjecture
    • Authors: Elchanan Mossel; Joe Neeman; Allan Sly
      Abstract: We study a random graph model called the “stochastic block model” in statistics and the “planted partition model” in theoretical computer science. In its simplest form, this is a random graph with two equal-sized classes of vertices, with a within-class edge probability of q and a between-class edge probability of q′. A striking conjecture of Decelle, Krzkala, Moore and Zdeborová [9], based on deep, non-rigorous ideas from statistical physics, gave a precise prediction for the algorithmic threshold of clustering in the sparse planted partition model. In particular, if q=a/n and q′=b/n, s=(a−b)/2 and d=(a+b)/2, then Decelle et al. conjectured that it is possible to efficiently cluster in a way correlated with the true partition if s 2>d and impossible if s 2<d. By comparison, until recently the best-known rigorous result showed that clustering is possible if s 2>Cdlnd for sufficiently large C. In a previous work, we proved that indeed it is information theoretically impossible to cluster if s 2 ≤ d and moreover that it is information theoretically impossible to even estimate the model parameters from the graph when s 2 < d. Here we prove the rest of the conjecture by providing an efficient algorithm for clustering in a way that is correlated with the true partition when s 2>d. A different independent proof of the same result was recently obtained by Massoulié [20].
      PubDate: 2017-08-14
      DOI: 10.1007/s00493-016-3238-8
       
 
 
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