Browsing by Author "Dalfó Simó, Cristina"
Now showing items 1-20 of 63
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A differential approach for bounding the index of graphs under perturbations
(2011-09-02)
Article
Open AccessThis paper presents bounds for the variation of the spectral radius (G) of a graph G after some perturbations or local vertex/edge modifications of G. The perturbations considered here are the connection of a new vertex ... -
A differential approach for bounding the index of graphs under perturbations
(2011-03)
External research report
Open Access -
Algebraic Characterizations of Regularity Properties in Bipartite Graphs
(2013)
Article
Restricted access - publisher's policyRegular and distance-regular characterizations of general graphs are well-known. In particular, the spectral excess theorem states that a connected graph GG is distance-regular if and only if its spectral excess (a number ... -
An algebraic approach to lifts of digraphs
(2018-12-07)
Article
Open AccessWe study the relationship between two key concepts in the theory of (di)graphs: the quotient digraph, and the lift Ga of a base (voltage) digraph. These techniques contract or expand a given digraph in order to study its ... -
A new general family of mixed graphs
(2019-01-11)
Article
Open AccessA new general family of mixed graphs is presented, which generalizes both the pancake graphs and the cycle prefix digraphs. The obtained graphs are vertex transitive and, for some values of the parameters, they constitute ... -
An improved upper bound for the order of mixed graphs
(2018-07)
Article
Open AccessA mixed graph G can contain both (undirected) edges and arcs (directed edges). Here we derive an improved Moore-like bound for the maximum number of vertices of a mixed graph with diameter at least three. Moreover, a ... -
A note on the order of iterated line digraphs
(Wiley, 2016-07-27)
Article
Open AccessGiven a digraph G, we propose a new method to find the recurrence equation for the number of vertices n_k of the k-iterated line digraph L_k(G), for k>= 0, where L_0(G) = G. We obtain this result by using the minimal polynomial ... -
A survey on the missing Moore graph
(Elsevier, 2019)
Article
Open AccessThis is a survey on some known properties of the possible Moore graph (or graphs) ¿ with degree 57 and diameter 2. Moreover, we give some new results about it, such as the following. When we consider the distance partition ... -
Characterizing identifying codes through the spectrum of a graph or digraph
(2017)
Conference report
Open Access -
Characterizing (l,m)-walk-regularity
(2009-05)
Article
Open AccessA graph $\G$ with diameter $D$ and $d+1$ distinct eigenvalues is said to be {\it $(\ell,m)$-walk-regular}, for some integers $\ell\in[0,d]$ and $m\in[0,D]$, $\ell\ge m$, if the number of walks of length $i\in [0,\ell]$ ... -
Cospectral digraphs from locally line digraphs
(Elsevier, 2016-07-01)
Article
Restricted access - publisher's policyA digraph Gamma = (V, E) is a line digraph when every pair of vertices u, v is an element of V have either equal or disjoint in -neighborhoods. When this condition only applies for vertices in a given subset (with at least ... -
Deterministic hierarchical networks
(2016)
Article
Open AccessIt has been shown that many networks associated with complex systems are small-world (they have both a large local clustering coefficient and a small diameter) and also scale-free (the degrees are distributed according ... -
Deterministic hierarchical networks
(2006)
Article
Open AccessIt has recently been shown that many networks associated with complex systems are small-world (they have both a large local clustering and a small average distance and diameter) and they are also scale-free (the degrees ... -
Deterministic hierarchical networks
(2007-11-20)
Article
Open AccessRecently it has been shown that many networks associated with complex systems are small-world (they have both a large local clustering and a small diameter) and they are also scale-free (the degrees are distributed according ... -
Dual concepts of almost distance-regularity and the spectral excess theorem
(Iniciativa Digital Politècnica, 2011)
Conference report
Open AccessGenerally speaking, ‘almost distance-regular’ graphs are graphs that share some, but not necessarily all, regularity properties that characterize distance-regular graphs. In this paper we first propose two dual concepts ... -
Edge distance-regular graphs
(2011)
Article
Open AccessEdge-distance-regularity is a concept recently introduced by the authors which is similar to that of distance-regularity, but now the graph is seen from each of its edges instead of from its vertices. More precisely, a ... -
Edge-distance-regular graphs
(2011)
Article
Restricted access - publisher's policyEdge-distance-regularity is a concept recently introduced by the authors which is similar to that of distance-regularity, but now the graph is seen from each of its edges instead of from its vertices. More precisely, a ... -
Edge-distance-regular graphs
(2011-03-11)
External research report
Open AccessEdge-distance-regularity is a concept recently introduced by the authors which is similar to that of distance-regularity, but now the graph is seen from each of its edges instead of from its vertices. More precisely, a ... -
Edge-distance-regular graphs are distance-regular
(2013)
Article
Restricted access - publisher's policyA graph is edge-distance-regular when it is distance-regular around each of its edges and it has the same intersection numbers for any edge taken as a root. In this paper we give some (combinatorial and algebraic) proofs ...
