Browsing by Author "Garriga Valle, Ernest"

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 
A new approach to the spectral excess theorem for distanceregular graphs
Fiol Mora, Miquel Àngel; Gago Álvarez, Silvia; Garriga Valle, Ernest (20090401)
Article
Open AccessThe Spectral Excess Theorem provides a quasispectral characterization for a (regular) graph $\Gamma$ with $d+1$ different eigenvalues to be distanceregular graph, in terms of the mean (d1)excess of its vertices.\ The ... 
Aprenentatge de càlcul
Aguiló Gost, Francisco de Asis L.; Barguilla Navarrete, Jorge; Garriga Valle, Ernest; Miralles de la Asunción, Alicia (Edicions UPC, 2002)
Book
Restricted access to the UPC academic communityConté: 1. Successions, continuïtat i derivació. 2. Integració i sèries. 
A simple proof of the spectral excess theorem for distanceregular graphs
Fiol Mora, Miquel Àngel; Gago Álvarez, Silvia; Garriga Valle, Ernest (Elsevier, 20100415)
Article
Restricted access  publisher's policyThe spectral excess theorem provides a quasispectral characterization for a (regular) graph Γ with d+1 distinct eigenvalues to be distanceregular graph, in terms of the excess (number of vertices at distance d) of each ... 
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 $i\in [0,\ell]$ ... 
Combinatorial vs. algebraic characterizations of pseudodistanceregularity around a set
Cámara Vallejo, Marc; Fàbrega Canudas, José; Fiol Mora, Miquel Àngel; Garriga Valle, Ernest (200906)
External research report
Open AccessGiven a simple connected graph $\Gamma$ and a subset of its vertices $C$, the pseudodistanceregularity around $C$ generalizes, for not necessarily regular graphs, the notion of completely regular code. Up to now, most ... 
Contribució a la teoria espectral de grafs problemes mètrics i distànciaregularitat
Garriga Valle, Ernest (Universitat Politècnica de Catalunya, 19971212)
Doctoral thesis
Open Access 
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 (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
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 ... 
Moments in graphs
Dalfó Simó, Cristina; Fiol Mora, Miquel Àngel; Garriga Valle, Ernest (2013)
Article
Open AccessLet G be a connected graph with vertex set V and a weight function that assigns a nonnegative number to each of its vertices. Then, the moment of G at vertex u is de ned to be M G(u) = P v2V (v) dist(u; v), where ... 
Number of walks and degree powers in a graph
Fiol Mora, Miquel Àngel; Garriga Valle, Ernest (200604)
Article
Open AccessThis letter deals with the relationship between the total number of kwalks in a graph, and the sum of the kth powers of its vertex degrees. In particular, it is shown that the sum of all kwalks is upper bounded by the ... 
On Almost DistanceRegular Graphs
Dalfó Simó, Cristina; Van Dam, Edwin; Fiol Mora, Miquel Àngel; Garriga Valle, Ernest; Gorissen, Bram (20100312)
External research report
Open Access 
On almost distanceregular graphs
Dalfó Simó, Cristina; Van Dam, Edwin; Fiol Mora, Miquel Àngel; Garriga Valle, Ernest; Gorissen, Bram (2010)
Article
Restricted access  publisher's policyDistanceregular graphs are a key concept in Algebraic Combinatorics and have given rise to several generalizations, such as association schemes. Motivated by spectral and other algebraic characterizations of distanceregular ... 
On kWalkRegular Graphs
Dalfó Simó, Cristina; Fiol Mora, Miquel Àngel; Garriga Valle, Ernest (200808)
Article
Open AccessConsidering a connected graph $G$ with diameter $D$, we say that it is \emph{$k$walkregular}, for a given integer $k$ $(0\leq k \leq D)$, if the number of walks of length $\ell$ between vertices $u$ and $v$ only depends ... 
On outindependent subgraphs of strongly regular graphs
Fiol Mora, Miquel Àngel; Garriga Valle, Ernest (Taylor & Francis, 2006)
Article
Open AccessAn outindependent subgraph of a graph G, with respect to an independent vertex subset C¿¿V, is the subgraph GC induced by the vertices in V\¿C. We study the case when G is strongly regular, where the results of de Caen ... 
On tcliques in kwalkregular graphs
Dalfó Simó, Cristina; Fiol Mora, Miquel Àngel; Garriga Valle, Ernest (200908)
Article
Restricted access  publisher's policyA graph is walkregular if the number of cycles of length rooted at a given vertex is a constant through all the vertices. For a walkregular graph G with d+1 different eigenvalues and spectrally maximum diameter D = ... 
On tcliques in kwalkregular graphs
Dalfó Simó, Cristina; Fiol Mora, Miquel Àngel; Garriga Valle, Ernest (Université de Bourdeaux, 2009)
Conference report
Open Access