Journal IssueDOI
Forcing highly connected subgraphs
TLDR
In this paper, a lower bound on the degree of vertices and the vertex-degree of the ends which is quadratic in k, the connectedness of the desired subgraph is given.Abstract:
A theorem of Mader states that highly connected subgraphs can be forced in finite graphs by assuming a high minimum degree. We extend this result to infinite graphs. Here, it is necessary to require not only high degree for the vertices but also high vertex-degree (or multiplicity) for the ends of the graph, that is, a large number of disjoint rays in each end. We give a lower bound on the degree of vertices and the vertex-degree of the ends which is quadratic in k, the connectedness of the desired subgraph. In fact, this is not far from best possible: we exhibit a family of graphs with a degree of order 2k at the vertices and a vertex-degree of order k log k at the ends which have no k-connected subgraphs.
Furthermore, if in addition to the high degrees at the vertices, we only require high edge-degree for the ends (which is defined as the maximum number of edge-disjoint rays in an end), Mader's theorem does not extend to infinite graphs, not even to locally finite ones. We give a counterexample in this respect. But, assuming a lower bound of at least 2k for the edge-degree at the ends and the degree at the vertices does suffice to ensure the existence (k + 1)-edge-connected subgraphs in arbitrary graphs. © 2006 Wiley Periodicals, Inc. J Graph Theory 54: 331–349, 2007read more
Citations
More filters
Journal ArticleDOI
Locally finite graphs with ends: A topological approach, I. Basic theory
TL;DR: This paper attempts to provide an entry point to this field for readers that have not followed the literature that has emerged in the last 10 years or so, and takes them on a quick route through what appear to be the most important lasting results, introduces them to key proof techniques, identifies the most promising open problems, and offers pointers to the literature for more detail.
Journal ArticleDOI
Uniqueness of electrical currents in a network of finite total resistance
TL;DR: In this article, it was shown that if the sum of the resistances of an electrical network N is finite, then there is a unique electrical current in N, provided that we do not allow any flow to escape to infinity.
Journal ArticleDOI
Locally finite graphs with ends: A topological approach, II. Applications
TL;DR: The topological approach has made it possible to extend to locally finite graphs many classical theorems of finite graph theory that do not extend verbatim, many of which solve problems or extend earlier work of Thomassen on infinite graphs.
Journal ArticleDOI
Graph topologies induced by edge lengths
TL;DR: The aim of this paper is to introduce |G|"@?
Journal ArticleDOI
Duality of ends
Henning Bruhn,Maya Stein +1 more
TL;DR: There exists a natural homeomorphism between the end spaces of a graph and its dual, and that preserves the ‘end degree’, and it is proved that Tutte-connectivity is invariant under taking (infinite) duals.
References
More filters
Journal ArticleDOI
Existenzn-fach zusammenhängender Teilgraphen in Graphen genügend großer Kantendichte
Journal ArticleDOI
The Cycle Space of an Infinite Graph
TL;DR: A new ‘singular’ approach is presented that builds the cycle space of a graph not on its finite cycles but on its topological circles, the homeomorphic images of $S^1$ in the space formed by the graph together with its ends.
Journal ArticleDOI
On end degrees and infinite cycles in locally finite graphs
Henning Bruhn,Maya Stein +1 more
TL;DR: It is proved that the edge set of a locally finite graph G lies in C(G) if and only if every vertex and every end has even degree.