### Enviaments recents

• #### Internally perfect matroids ﻿

(2017-06-16)
Article
Accés obert
In 1977 Stanley proved that the $h$-vector of a matroid is an $\mathcal{O}$-sequence and conjectured that it is a pure $\mathcal{O}$-sequence. In the subsequent years the validity of this conjecture has been shown for a ...
• #### Stabbing segments with rectilinear objects ﻿

(2017-09-15)
Article
Accés obert
Given a set S of n line segments in the plane, we say that a region R¿R2 is a stabber for S if R contains exactly one endpoint of each segment of S. In this paper we provide optimal or near-optimal algorithms for ...
• #### On perfect and quasiperfect dominations in graphs ﻿

(2017-02-27)
Article
Accés obert
A subset S ¿ V in a graph G = ( V , E ) is a k -quasiperfect dominating set (for k = 1) if every vertex not in S is adjacent to at least one and at most k vertices in S . The cardinality of a minimum k -quasiperfect ...
• #### Stabbing circles for sets of segments in the plane ﻿

(2017-03-13)
Article
Accés obert
Stabbing a set S of n segments in the plane by a line is a well-known problem. In this paper we consider the variation where the stabbing object is a circle instead of a line. We show that the problem is tightly connected ...
• #### General properties of c-circulant digraphs ﻿

(1988)
Article
Accés obert
A digraph is said to be a c-circulant if its adjacency matrix is c-circulant. This paper deals with general properties of this family of digraphs, as isomorphisms, regularity, strong connectivity, diameter and the relation ...
• #### Production matrices for geometric graphs ﻿

(2016)
Article
Accés restringit per política de l'editorial
We present production matrices for non-crossing geometric graphs on point sets in convex position, which allow us to derive formulas for the numbers of such graphs. Several known identities for Catalan numbers, Ballot ...
• #### New results on stabbing segments with a polygon ﻿

(2015-01-01)
Article
Accés obert
We consider a natural variation of the concept of stabbing a set of segments with a simple polygon: a segment s is stabbed by a simple polygon P if at least one endpoint of s is contained in P, and a segment set S is stabbed ...
• #### Adjacency-preserving spatial treemaps ﻿

(2016)
Article
Accés obert
Rectangular layouts, subdivisions of an outer rectangle into smaller rectangles, have many applications in visualizing spatial information, for instance in rectangular cartograms in which the rectangles represent geographic ...
• #### Widening the analysis of Energy Return On Investment (EROI) in agroecosystems: A proposal to study socio-ecological transitions to industrialized farm systems (the Vallès County, Catalonia, c.1860 and 1999) ﻿

(2016)
Article
Accés restringit per política de l'editorial
Energy balances of farm systems have overlooked the role of energy flows that remain within agro-ecosystems. Yet, such internal flows fulfil important socio-ecological functions, including maintenance of farmers themselves ...
• #### Computing the canonical representation of constructible sets ﻿

(2016-03-08)
Article
Accés obert
Constructible sets are needed in many algorithms of Computer Algebra, particularly in the GröbnerCover and other algorithms for parametric polynomial systems. In this paper we review the canonical form ofconstructible sets ...