Browsing by Author "Dalfó Simó, Cristina"

A differential approach for bounding the index of graphs under perturbations
Dalfó Simó, Cristina; Fiol Mora, Miquel Àngel; Garriga Valle, Ernest (20110902)
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
Dalfó Simó, Cristina; Fiol Mora, Miquel Àngel; Garriga Valle, Ernest (201103)
External research report
Open Access 
Algebraic Characterizations of Regularity Properties in Bipartite Graphs
Abiad Monge, Aida; Dalfó Simó, Cristina; Fiol Mora, Miquel Àngel (2013)
Article
Restricted access  publisher's policyRegular and distanceregular characterizations of general graphs are wellknown. In particular, the spectral excess theorem states that a connected graph GG is distanceregular if and only if its spectral excess (a number ... 
An algebraic approach to lifts of digraphs
Dalfó Simó, Cristina; Fiol Mora, Miquel Àngel; Miller, Mirka; Ryan, Joe; Siran, Josef (20181207)
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
Dalfó Simó, Cristina (20190111)
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
Dalfó Simó, Cristina; Fiol Mora, Miquel Àngel; López Lorenzo, Nacho (201807)
Article
Open AccessA mixed graph G can contain both (undirected) edges and arcs (directed edges). Here we derive an improved Moorelike 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
Dalfó Simó, Cristina; Fiol Mora, Miquel Àngel (Wiley, 20160727)
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 kiterated 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
Dalfó Simó, Cristina (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
Balbuena Martínez, Maria Camino Teófila; Dalfó Simó, Cristina; Martínez Barona, Berenice (2017)
Conference report
Open Access 
Characterizing (l,m)walkregularity
Dalfó Simó, Cristina; Fiol Mora, Miquel Àngel; Garriga Valle, Ernest (200905)
Article
Open AccessA graph $\G$ with diameter $D$ and $d+1$ distinct eigenvalues is said to be {\it $(\ell,m)$walkregular}, for some integers $\ell\in[0,d]$ and $m\in[0,D]$, $\ell\ge m$, if the number of walks of length $i\in [0,\ell]$ ... 
Corrigendum to "Algebraic characterizations of regularity properties in bipartite graphs" Eur. J. Combin. 34 (2013) 12231231
Abiad Monge, Aida; Dalfó Simó, Cristina; Fiol Mora, Miquel Àngel (2014)
Article
Open Access 
Cospectral digraphs from locally line digraphs
Dalfó Simó, Cristina; Fiol Mora, Miquel Àngel (Elsevier, 20160701)
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
Barrière Figueroa, Eulalia; Comellas Padró, Francesc de Paula; Dalfó Simó, Cristina; Fiol Mora, Miquel Àngel (2016)
Article
Open AccessIt has been shown that many networks associated with complex systems are smallworld (they have both a large local clustering coefficient and a small diameter) and also scalefree (the degrees are distributed according ... 
Deterministic hierarchical networks
Barrière Figueroa, Eulalia; Comellas Padró, Francesc de Paula; Dalfó Simó, Cristina (2006)
Article
Open AccessIt has recently been shown that many networks associated with complex systems are smallworld (they have both a large local clustering and a small average distance and diameter) and they are also scalefree (the degrees ... 
Deterministic hierarchical networks
Barrière Figueroa, Eulalia; Comellas Padró, Francesc de Paula; Dalfó Simó, Cristina; Fiol Mora, Miquel Àngel (20071120)
Article
Open AccessRecently it has been shown that many networks associated with complex systems are smallworld (they have both a large local clustering and a small diameter) and they are also scalefree (the degrees are distributed according ... 
Dual concepts of almost distanceregularity and the spectral excess theorem
Dalfó Simó, Cristina; Fiol Mora, Miquel Àngel; Garriga Valle, Ernest; Dam, Edwin R. van (Iniciativa Digital Politècnica, 2011)
Conference report
Open AccessGenerally speaking, ‘almost distanceregular’ graphs are graphs that share some, but not necessarily all, regularity properties that characterize distanceregular graphs. In this paper we first propose two dual concepts ... 
Edge distanceregular graphs
Cámara Vallejo, Marc; Dalfó Simó, Cristina; Fàbrega Canudas, José; Fiol Mora, Miquel Àngel; Garriga Valle, Ernest (2011)
Article
Open AccessEdgedistanceregularity is a concept recently introduced by the authors which is similar to that of distanceregularity, but now the graph is seen from each of its edges instead of from its vertices. More precisely, a ... 
Edgedistanceregular graphs
Cámara Vallejo, Marc; Dalfó Simó, Cristina; Fàbrega Canudas, José; Fiol Mora, Miquel Àngel; Garriga Valle, Ernest (2011)
Article
Restricted access  publisher's policyEdgedistanceregularity is a concept recently introduced by the authors which is similar to that of distanceregularity, but now the graph is seen from each of its edges instead of from its vertices. More precisely, a ... 
Edgedistanceregular graphs
Cámara Vallejo, Marc; Dalfó Simó, Cristina; Fàbrega Canudas, José; Fiol Mora, Miquel Àngel; Garriga Valle, Ernest (20110311)
External research report
Open AccessEdgedistanceregularity is a concept recently introduced by the authors which is similar to that of distanceregularity, but now the graph is seen from each of its edges instead of from its vertices. More precisely, a ... 
Edgedistanceregular graphs are distanceregular
Cámara Vallejo, Marc; Dalfó Simó, Cristina; Delorme, Charles; Fiol Mora, Miquel Àngel; Suzuki, Hiroshi (2013)
Article
Restricted access  publisher's policyA graph is edgedistanceregular when it is distanceregular 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 ...