REED , Bruce

International audience

In this contribution, we investigate the giant component problem in random graphs with a given degree sequence. We generalize the critical condition of Molloy and Reed [Molloy, M., and B. Reed, A critical point for random graphs with given degree sequence, Random Structures Algorithms 6 (1995), 161-179], which determines the existence of a...

Given a branching random walk, let $M_n$ be the minimum position of any member of the $n$th generation. We calculate $\\mathbfEM_n$ to within O(1) and prove exponential tail bounds for $\\mathbfP{|M_n-\\mathbfEM_n|>x}$, under quite general conditions on the branching random walk. In particular, together with work by Bramson [Z. Wahrsch. Verw....

In this paper we prove the following result. Suppose that s and t are vertices of a 3-connected graph G such that G-s-t is not bipartite and there is no cutset X of size three in G for which some component U of G-X is disjoint from s,t. Then either (1) G contains an induced path P from s to t such that G-V(P) is not bipartite or (2) G can be...

For any c>1, we describe a linear time algorithm for fractionally edge colouring simple graphs with maximum degree at least |V|/c.

An L(p,1)-labeling of a graph is a function f from the vertex set to the positive integers such that |f(x) − f(y)| ≥ p if dist(x, y) = 1 and |f(x) − f(y)| ≥ 1 if dist(x, y) = 2, where dist(x,y) is the distance between the two vertices x and y in the graph. The span of an L(p,1)- labeling f is the difference between the largest and the smallest...

An $L(2,1)$-labelling of a graph is a function $f$ from the vertex set to the positive integers such that $|f(x)-f(y)|\geq 2$ if $dist(x,y)=1$ and $|f(x)-f(y)|\geq 1$ if $dist(x,y)=2$, where $dist(u,v)$ is the distance between the two vertices~$u$ and~$v$ in the graph $G$. The \emph{span} of an $L(2,1)$-labelling $f$ is the difference between...

International audience

A well-known conjecture of Erdős and Sós states that every graph with average degree exceeding $m−1$ contains every tree with m edges as a subgraph. We propose a variant of this conjecture, which states that every graph of maximum degree exceeding m and minimum degree at least $[\frac{2m}{3}]$ contains every tree with m edges. As evidence for...

International audience

In 1977, Wegner conjectured that the chromatic number of the square of every planar graph~$G$ with maximum degree $\Delta\ge8$ is at most $\bigl\lfloor\frac32\,\Delta\bigr\rfloor+1$. We show that it is at most $\frac32\,\Delta\,(1+o(1))$, and indeed this is true for the list chromatic number and for more general classes of graphs.

International audience

A Kl-expansion consists of l vertex-disjoint trees, every two of which are joined by an edge. We call such an expansion odd if its vertices can be two-coloured so that the edges of the trees are bichromatic but the edges between trees are monochromatic. We show that, for every l, if a graph contains no odd Kl-expansion then its chromatic number...

Let $f(k)$ be the smallest integer such that every $f(k)$-chromatic digraph contains every oriented tree of order $k$. Burr proved $f(k)\leq (k-1)^2$ in general, and he conjectured $f(k)=2k-2$. Burr also proved that every $(8k-7)$-chromatic digraph contains every antidirected tree. We improve both of Burr's bounds. We show that $f(k)\leq...

Let f (k) be the smallest integer such that every f (k)-chromatic digraph contains every oriented tree of order k. Burr proved that f (k) ≤ (k − 1)^2 and conjectured f (k) = 2n − 2. In this paper, we give some sufficient conditions for an n-chromatic digraphs to contains some oriented tree. In particular, we show that every acyclic n-chromatic...