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2. Total positivity of Toeplitz matrices of recursive hypersequencesTomislav Došlić, Ivica Martinjak, Riste Škrekovski, 2019, original scientific article Keywords: total positivity, totally positive matrix, Toeplitz matrix, Hankel matrix, hyperfibonacci sequence, log-concavity Published in RUP: 03.01.2022; Views: 803; Downloads: 25 Full text (254,44 KB) |
3. On [plus/minus] 1 eigenvectors of graphsDragan Stevanović, 2016, original scientific article Abstract: While discussing his spectral bound on the independence number of a graph, Herbert Wilf asked back in 1986 what kind of a graph admits an eigenvector consisting solely of ▫$\pm 1$▫ entries? We prove that Wilf's problem is NP-complete, but also that the set of graphs having a ▫$\pm 1$▫ eigenvector is quite rich, being closed under a number of different graph compositions. Keywords: eigenvector, adjacency matrix, Wilf's problem Published in RUP: 03.01.2022; Views: 726; Downloads: 26 Full text (325,02 KB) |
4. On minimal forbidden subgraphs for the class of EDM-graphsGašper Jaklič, Jolanda Modic, 2015, original scientific article Abstract: In this paper, a relation between graph distance matrices and Euclidean distance matrices (EDM) is considered. Graphs, for which the distance matrix is not an EDM (NEDM-graphs), are studied. All simple connected non-isomorphic graphs on ▫$n \le 8$▫ nodes are analysed and a characterization of the smallest NEDM-graphs, i.e., the minimal forbidden subgraphs, is given. It is proven that bipartite graphs and some subdivisions of the smallest NEDM-graphs are NEDM-graphs, too. Keywords: graph theory, graph, Euclidean distance matrix, distance, eigenvalue Published in RUP: 31.12.2021; Views: 928; Downloads: 19 Full text (711,65 KB) |
5. Commuting graphs and extremal centralizersGregor Dolinar, Aleksandr Èmilevič Guterman, Bojan Kuzma, Polona Oblak, 2014, original scientific article Abstract: We determine the conditions for matrix centralizers which can guarantee the connectedness of the commuting graph for the full matrix algebra ▫$M_n(\mathbb{F})$▫ over an arbitrary field ▫$\mathbb{F}$▫. It is known that if ▫$\mathbb{F}$▫ is an algebraically closed field and ▫$n \ge 3$▫, then the diameter of the commuting graph of ▫$M_n(\mathbb{F})$▫ is always equal to four. We construct a concrete example showing that if ▫$\mathbb{F}$▫ is not algebraically closed, then the commuting graph of ▫$M_n(\mathbb{F})$▫ can be connected with the diameter at least five. Keywords: commuting graph, matrix ring, centralizer Published in RUP: 31.12.2021; Views: 796; Downloads: 23 Full text (228,78 KB) |
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9. O ekstremnih grafih z dano stopnjo in premerom/ožino : doktorska disertacijaSlobodan Filipovski, 2018, doctoral dissertation Keywords: adjacency matrix, antipodal graphs, cages, excess, defect, Ramanujan graphs, selfrepeats, degree/diameter problem, spectrum, Moore graphs, asymptotic density, distance matrices, Bermond and Bollobas problem Published in RUP: 21.01.2019; Views: 2632; Downloads: 0 |
10. Mamart, Siwaporn: A group commutator involving the last distance matrix and dual distance matrix of a Q-polynomial distance-regular graph: the Hamming graph case. - Graphs Combin. 34 (2018), no. 4, 803--817Safet Penjić, 2018, review, book review, critique Keywords: distance-regular graph, Q-polynomial, distance matrix, dual distance matrix Published in RUP: 21.01.2019; Views: 1512; Downloads: 15 Link to full text |