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Arbology: Trees and pushdown automata

Bořivoj Melichar, Jan Janoušek, Tomas Flouri (2012)

Kybernetika

We present a unified and systematic approach to basic principles of Arbology, a new algorithmic discipline focusing on algorithms on trees. Stringology, a highly developed algorithmic discipline in the area of string processing, can use finite automata as its basic model of computation. For various kinds of linear notations of ranked and unranked ordered trees it holds that subtrees of a tree in a linear notation are substrings of the tree in the linear notation. Arbology uses pushdown automata...

Arboreal structure and regular graphs of median-like classes

Bostjan Brešar (2003)

Discussiones Mathematicae Graph Theory

We consider classes of graphs that enjoy the following properties: they are closed for gated subgraphs, gated amalgamation and Cartesian products, and for any gated subgraph the inverse of the gate function maps vertices to gated subsets. We prove that any graph of such a class contains a peripheral subgraph which is a Cartesian product of two graphs: a gated subgraph of the graph and a prime graph minus a vertex. Therefore, these graphs admit a peripheral elimination procedure which is a generalization...

Arbres minimals i arbres de Steiner en la mètrica rectilínea.

Josep M. Basart, Llorenç Huguet (1988)

Qüestiió

Usando la métrica rectilínea (oL1) se tratan algunos aspectos del problema clásico de hallar el árbol de coste mínimo que enlaza un conjunto dado de P puntos en el plano.En primer lugar se recuerdan las propiedades fundamentales de los árboles de Steiner dado que éstos son la solución general al problema enunciado. A partir de unas observaciones sobre la acotación de su longitud máxima cuando P se halla en el interior de un cuadrado Q de lado unidad, se obtiene -para el mismo caso- una cota superior...

Arc-transitive and s-regular Cayley graphs of valency five on Abelian groups

Mehdi Alaeiyan (2006)

Discussiones Mathematicae Graph Theory

Let G be a finite group, and let 1 G ∉ S ⊆ G . A Cayley di-graph Γ = Cay(G,S) of G relative to S is a di-graph with a vertex set G such that, for x,y ∈ G, the pair (x,y) is an arc if and only if y x - 1 ∈ S . Further, if S = S - 1 : = s - 1 | s ∈ S , then Γ is undirected. Γ is conected if and only if G = ⟨s⟩. A Cayley (di)graph Γ = Cay(G,S) is called normal if the right regular representation of G is a normal subgroup of the automorphism group of Γ. A graph Γ is said to be arc-transitive, if Aut(Γ) is transitive on an arc set. Also, a graph Γ...

Arithmetic labelings and geometric labelings of countable graphs

Gurusamy Rengasamy Vijayakumar (2010)

Discussiones Mathematicae Graph Theory

An injective map from the vertex set of a graph G-its order may not be finite-to the set of all natural numbers is called an arithmetic (a geometric) labeling of G if the map from the edge set which assigns to each edge the sum (product) of the numbers assigned to its ends by the former map, is injective and the range of the latter map forms an arithmetic (a geometric) progression. A graph is called arithmetic (geometric) if it admits an arithmetic (a geometric) labeling. In this article, we show...

Arithmetically maximal independent sets in infinite graphs

Stanisław Bylka (2005)

Discussiones Mathematicae Graph Theory

Families of all sets of independent vertices in graphs are investigated. The problem how to characterize those infinite graphs which have arithmetically maximal independent sets is posed. A positive answer is given to the following classes of infinite graphs: bipartite graphs, line graphs and graphs having locally infinite clique-cover of vertices. Some counter examples are presented.

Associative graph products and their independence, domination and coloring numbers

Richard J. Nowakowski, Douglas F. Rall (1996)

Discussiones Mathematicae Graph Theory

Associative products are defined using a scheme of Imrich & Izbicki [18]. These include the Cartesian, categorical, strong and lexicographic products, as well as others. We examine which product ⊗ and parameter p pairs are multiplicative, that is, p(G⊗H) ≥ p(G)p(H) for all graphs G and H or p(G⊗H) ≤ p(G)p(H) for all graphs G and H. The parameters are related to independence, domination and irredundance. This includes Vizing's conjecture directly, and indirectly the Shannon capacity of a graph...

Asteroidal Quadruples in non Rooted Path Graphs

Marisa Gutierrez, Benjamin Lévêque, Silvia B. Tondato (2015)

Discussiones Mathematicae Graph Theory

A directed path graph is the intersection graph of a family of directed subpaths of a directed tree. A rooted path graph is the intersection graph of a family of directed subpaths of a rooted tree. Rooted path graphs are directed path graphs. Several characterizations are known for directed path graphs: one by forbidden induced subgraphs and one by forbidden asteroids. It is an open problem to find such characterizations for rooted path graphs. For this purpose, we are studying in this paper directed...

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