منابع مشابه
On almost distance-regular graphs
Distance-regular graphs have been a key concept in Algebraic Combinatorics and have given place to several generalizations, such as association schemes. Motivated by spectral and other algebraic characterizations of distance-regular graphs, we study ‘almost distance-regular graphs’. We use this name informally for graphs that share some regularity properties that are related to distance in the ...
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We give lower bounds on the largest singular value of arbitrary matrices, some of which are asymptotically tight for almost all matrices. To study when these bounds are exact, we introduce several combinatorial concepts. In particular, we introduce regular, pseudo-regular, and almost regular matrices. Nonnegative, symmetric, almost regular matrices were studied earlier by Ho¤man, Wolfe, and Ho¤...
متن کاملAlmost Regular Bundles on Del Pezzo Fibrations
This paper is devoted to the study of a certain class of principal bundles on del Pezzo surfaces, which were introduced and studied by Friedman and Morgan in [10]: The two authors showed that there exists a unique principal bundle (up to isomorphism) on a given (Gorenstein) del Pezzo surface satisfying certain properties. We call these bundles almost regular. In turn, we study them in families....
متن کاملOn maximum matchings in almost regular graphs
In 2010, Mkrtchyan, Petrosyan and Vardanyan proved that every graph G with 2 ≤ δ(G) ≤ ∆(G) ≤ 3 contains a maximum matching whose unsaturated vertices do not have a common neighbor, where ∆(G) and δ(G) denote the maximum and minimum degrees of vertices in G, respectively. In the same paper they suggested the following conjecture: every graph G with ∆(G)− δ(G) ≤ 1 contains a maximum matching whos...
متن کاملOn Almost-Regular Edge Colourings of Hypergraphs
We prove that if H = (V (H), E(H)) is a hypergraph, γ is an edge colouring of H, and S ⊆ V (H) such that any permutation of S is an automorphism of H, then there exists a permutation π of E(H) such that |π(E)| = |E| and π(E)\S = E \S for each E ∈ E(H), and such that the edge colouring γ′ of H given by γ′(E) = γ(π−1(E)) for each E ∈ E(H) is almost regular on S. The proof is short and elementary....
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ژورنال
عنوان ژورنال: CYTOLOGIA
سال: 1939
ISSN: 0011-4545,1348-7019
DOI: 10.1508/cytologia.9.412