@w3.sdu.edu.tr
Mathematics
Süleyman Demirel University
Discrete Mathematics and Combinatorics, Geometry and Topology
Scopus Publications
Scholar Citations
Scholar h-index
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Yusuf Civan, Zakir Deniz, and Mehmet Akif Yetim
Elsevier BV
Yusuf Civan, Zakir Deniz, and Mehmet Akif Yetim
Springer Science and Business Media LLC
Yusuf Civan
Springer Science and Business Media LLC
Yusuf Civan, Zakir Deniz, and Mehmet Akif Yetim
Elsevier BV
Turker Biyikouglu and Yusuf Civan
Rocky Mountain Mathematics Consortium
Türker Biyikoğlu and Yusuf Civan
Springer Science and Business Media LLC
Yusuf CİVAN and Demet TAYLAN
The Scientific and Technological Research Council of Turkey (TUBITAK-ULAKBIM) - DIGITAL COMMONS JOURNALS
Given a graph G with an induced subgraph H and a family F of graphs, we introduce a (hyper)graph HH(G;F)=(VH, EH), the hyper-H (hyper)graph of G with respect to F, whose vertices are induced copies of H in G, and \\{H1,H2,\\ldots,Hr\\} \\in EH if and only if the induced subgraph of G by the set \\cupi=1r Hi is isomorphic to a graph F in the family F, and the integer r is the least integer for F with this property. When H is a k-complete or a k-path of G, we abbreviate HKk(G;F) and HPk(G;F) to Hk(G;F) and HPk(G;F), respectively. Our motivation to introduce this new (hyper)graph operator on graphs comes from the fact that the graph Hk(Kn;\\{K2k\\}) is isomorphic to the ordinary Kneser graph K(n;k) whenever 2k \\leq n. As a generalization of the Lovasz--Kneser theorem, we prove that c(Hk(G;\\{K2k\\}))=c(G)-2k+2 for any graph G with w(G)=c(G) and any integer k\\leq \\lfloor w(G)/2\\rfloor. We determine the clique and fractional chromatic numbers of Hk(G;\\{K2k\\}), and we consider the generalized Johnson graphs Hr(H;\\{Kr+1\\}) and show that c(Hr(H;\\{Kr+1\\}))\\leq c(H) for any graph H and any integer r< w(H). By way of application, we construct examples of graphs such that the gap between their chromatic and fractional chromatic numbers is arbitrarily large. We further analyze the chromatic number of hyperpath (hyper)graphs HPk(G;Pm), and we provide upper bounds when m=k+1 and m=2k in terms of the k-distance chromatic number of the source graph.
Yusuf Civan
Springer Science and Business Media LLC
Türker Bıyıkoğlu and Yusuf Civan
Springer Science and Business Media LLC
Yusuf Civan
Akademiai Kiado Zrt.
We introduce linear Sperner families and lattices, and provide some open problems.
Yusuf Civan and Ergün Yalçın
Elsevier BV
Yusuf Civan
American Mathematical Society (AMS)
We study the enumeration problem of stably complex structures on bounded flag manifolds arising from omniorientations, and determine those induced by almost complex structures. We also enumerate the stably complex structures on these manifolds which bound, therefore representing zero in the complex cobordism ring Ω ∗ U \\Omega _*^U .
Yusuf Civan
Springer Science and Business Media LLC
Yusuf Civan and Nigel Ray
Portico