جستجوی مقالات مرتبط با کلیدواژه « Distance spectrum » در نشریات گروه « ریاضی »

The distance eigenvalues of a connected graph $G$ are the eigenvalues of its distance matrix‎‎$D(G)$‎. ‎A graph is called distance integral if all of its‎‎distance eigenvalues are integers.‎‎Let $n$ and $k$ be integers with $n>2k‎, ‎kgeq1$‎. ‎The bipartite Kneser graph $H(n,k)$ is the graph with the set of all $k$ and $n-k$ subsets of the set $[n]={1,2,...,n}$ as vertices‎, ‎in which two vertices are adjacent if and only if one of them is a subset of the other‎. ‎In this paper‎, ‎we determine the distance spectrum of $H(n,1)$‎. ‎Although the obtained result is not new cite{12}‎, ‎but our proof is new‎. ‎The main tool that we use in our work is the orbit partition method in algebraic graph theory for finding the eigenvalues of graphs‎. ‎We introduce a new method for‎‎determining the distance spectrum of $H(n,1)$ and show how‎‎a quotient matrix can contain all distance eigenvalues of‎‎a graph.‎

Let $G$ be a connected graph with vertex set $V(G)={v_1, v_2,ldots,v_n}$‎. ‎The distance matrix $D=D(G)$ of $G$ is defined so that its $(i,j)$-entry is equal to the distance $d_G(v_i,v_j)$ between the vertices $v_i$ and $v_j$ of $G$‎. ‎The eigenvalues ${mu_1, mu_2,ldots,mu_n}$ of $D(G)$ are the $D$-eigenvalues of $G$ and form the distance spectrum or the $D$-spectrum of $G$‎, ‎denoted by $Spec_D(G)$‎. ‎In this paper‎, ‎we introduce two new operations $G_1blacksquare_k G_2$ and $G_1blacklozenge_k G_2$ on graphs $G_1$ and $G_2$‎, ‎and describe the distance spectra of $G_1blacksquare_k G_2$ and $G_1blacklozenge_k G_2$ of regular graphs $G_1$ and $G_2 $ in terms of their adjacency spectra‎. ‎By using these results‎, ‎we obtain some new integral adjacency spectrum graphs‎, ‎integral distance spectrum graphs and a number of families of sets of noncospectral graphs with equal distance energy‎.

The D-eigenvalues {µ1,…,µp} of a graph G are the eigenvalues of its distance matrix D and form its D-spectrum. The D-energy, ED(G) of G is given by ED (G) =∑i=1p |µi|. Two non cospectral graphs with respect to D are said to be D-equi energetic if they have the same D-energy. In this paper we show that if G is an r-regular graph on p vertices with 2r ≤ p - 1, then the complements of iterated line graphs of G are of diameter 2 and that ED(\overline{Lk(G)}), k≥2 depends only on p and r. This result leads to the construction of regular D-equi energetic pair of graphs.