Selected Topics from the Theory of Graph Energy: Hypoenergetic Graph
Selections and weak orderability
We answer a question of van Mill and Wattel by showing that there is a separable locally compact space which admits a continuous weak selection but is not weakly orderable. Furthermore, we show that a separable space which admits a continuous weak selection can be covered by two weakly orderable spaces. Finally, we give a partial answer to a question of Gutev and Nogura by showing that a separable space which admits a continuous weak selection admits a continuous selection for all finite sets.
Self-complementary hypergraphs
A k-uniform hypergraph H = (V;E) is called self-complementary if there is a permutation σ:V → V, called self-complementing, such that for every k-subset e of V, e ∈ E if and only if σ(e) ∉ E. In other words, H is isomorphic with . In the present paper, for every k, (1 ≤ k ≤ n), we give a characterization of self-complementig permutations of k-uniform self-complementary hypergraphs of the order n. This characterization implies the well known results for self-complementing permutations of graphs,...
Self-complementary vertex-transitive undirected graphs
Self-derived polar graphs
Self-describing sequences and the Catalan family tree.
Self-diclique circulant digraphs
We study a particular digraph dynamical system, the so called digraph diclique operator. Dicliques have frequently appeared in the literature the last years in connection with the construction and analysis of different types of networks, for instance biochemical, neural, ecological, sociological and computer networks among others. Let be a reflexive digraph (or network). Consider and (not necessarily disjoint) nonempty subsets of vertices (or nodes) of . A disimplex of is the subdigraph...
Self-dual non-Hamiltonian polyhedra with only two types of faces
Self-dual planar hypergraphs and exact bond percolation thresholds.
Self-dual regular maps from medial graphs.
Self-invariant 1-factorizations of complete graphs and finite Bol loops of exponent 2.
Semidefinite functions on categories.
Semi-definite positive programming relaxations for graph K-coloring in frequency assignment
In this paper we will describe a new class of coloring problems, arising from military frequency assignment, where we want to minimize the number of distinct -uples of colors used to color a given set of -complete-subgraphs of a graph. We will propose two relaxations based on Semi-Definite Programming models for graph and hypergraph coloring, to approximate those (generally) NP-hard problems, as well as a generalization of the works of Karger et al. for hypergraph coloring, to find good feasible...
Semi-Definite positive Programming Relaxations for Graph Kn-Coloring in Frequency Assignment
In this paper we will describe a new class of coloring problems, arising from military frequency assignment, where we want to minimize the number of distinct n-uples of colors used to color a given set of n-complete-subgraphs of a graph. We will propose two relaxations based on Semi-Definite Programming models for graph and hypergraph coloring, to approximate those (generally) NP-hard problems, as well as a generalization of the works of Karger et al. for hypergraph coloring, to find good feasible...
Semidefinite programming and combinatorial optimization.
Semidomatic and total semidomatic numbers of directed graphs
Certain numerical invariants of directed graphs, analogous to the domatic number and to the total domatic number of an undirected graph, are introduced and studied.
Semidomatic numbers of directed graphs
Semigroups of mappings on graphs.
Semigroups over trees.
Semisymmetric cubic graphs of order .