12 research outputs found
An Ehrhart theoretic approach to generalized Golomb rulers
A Golomb ruler is a sequence of integers whose pairwise differences, or
equivalently pairwise sums, are all distinct. This definition has been
generalized in various ways to allow for sums of h integers, or to allow up to
g repetitions of a given sum or difference. Beck, Bogart, and Pham applied the
theory of inside-out polytopes of Beck and Zaslavsky to prove structural
results about the counting functions of Golomb rulers. We extend their approach
to the various types of generalized Golomb rulers.Comment: 15 pages, 2 figure
Bivariate Chromatic Polynomials of Mixed Graphs
The bivariate chromatic polynomial of a graph ,
introduced by Dohmen-P\"{o}nitz-Tittmann (2003), counts all -colorings of
such that adjacent vertices get different colors if they are . We
extend this notion to mixed graphs, which have both directed and undirected
edges. Our main result is a decomposition formula which expresses
as a sum of bivariate order polynomials (Beck-Farahmand-Karunaratne-Zuniga Ruiz
2020), and a combinatorial reciprocity theorem for .Comment: 10 pages, 3 figures, Revised according to referee comment
Hopf algebraic structures on mixed graphs
We introduce two coproducts on mixed graphs (that is to say graphs with both
edges and arcs), the first one by separation of the vertices into two parts,
and the second one given by contraction and extractions of subgraphs. We show
that, with the disjoint union product, this gives a double bialgebra, that is
to say that the first coproduct makes it a Hopf algebra in the category of righ
comodules over the second coproduct. This structures implies the existence of a
unique polynomial invariants on mixed graphs compatible with the product and
both coproducts: we prove that it is the (strong) chromatic polynomial of Beck,
Bogart and Pham. Using the action of the monoid of characters, we relate it to
the weak chromatic polynomial, as well to Ehrhart polynomials and to a
polynomial invariants related to linear extensions. As applications, we give an
algebraic proof of the link between the values of the strong chromatic
polynomial at negative values and acyclic orientations (a result due to Beck,
Blado, Crawford, Jean-Louis and Young) and obtain a combinatorial description
of the antipode of the Hopf algebra of mixed graphs
Global Constraint Catalog, 2nd Edition
This report presents a catalogue of global constraints where
each constraint is explicitly described in terms of graph properties and/or automata and/or first order logical formulae with arithmetic. When available, it also presents some typical usage as well as some pointers to existing
filtering algorithms
Global Constraint Catalog, 2nd Edition (revision a)
This report presents a catalogue of global constraints where
each constraint is explicitly described in terms of graph properties and/or automata and/or first order logical formulae with arithmetic. When available, it also presents some typical usage as well as some pointers to existing
filtering algorithms