Trimming weighted graphs of bounded treewidth

Recoloring bounded treewidth graphs

Let k be an integer. Two vertex k-colorings of a graph are adjacent if they differ on exactly one vertex. A graph is k-mixing if any proper k-coloring can be transformed into any other through a sequence of adjacent proper k-colorings. Any graph is (tw + 2)-mixing, where tw is the treewidth of the graph (Cereceda 2006). We prove that the shortest sequence between any two (tw + 2)-colorings is a...

On bounded treewidth duality of graphs

Channel assignment on graphs of bounded treewidth

The following ‘constraint matrix span problem’ arises in the assignment of radio channels in cellular communications systems. Given a graph G with a positive integer length l(xy) for each edge xy, and given a positive integer B, can we assign to each vertex x a channel (x) from 1; : : : ; B such that | (x)− (y)|¿ l(xy) for each edge xy? We show that this problem is NP-complete for graphs of tre...

Defensive Alliances in Graphs of Bounded Treewidth

A set S of vertices of a graph is a defensive alliance if, for each element of S, the majority of its neighbors is in S. The problem of finding a defensive alliance of minimum size in a given graph is NP-hard and there are polynomial-time algorithms if certain parameters are bounded by a fixed constant. In particular, fixed-parameter tractability results have been obtained for some structural p...

Randomly coloring graphs of bounded treewidth

We consider the problem of sampling a proper k-coloring of a graph of maximal degree ∆ uniformly at random. We describe a new Markov chain for sampling colorings, and show that it mixes rapidly on graphs of bounded treewidth if k ≥ (1 + )∆, for any > 0.