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On the connectivity of visibility graphs

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Degenerate crossing numbers

János Pach

Let G be a graph with n vertices and ea parts per thousand yen4n edges, drawn in the plane in such a way that if two or more edges (arcs) share an interior point p, then they properly cross one another at p. It is shown that the number of crossing points, ...

Springer-Verlag2009

Degree-constrained edge partitioning in graphs arising from discrete tomography

Dominique de Werra, Bernard Ries

Starting from the basic problem of reconstructing a 2-dimensional image given by its projections on two axes, one associates a model of edge coloring in a complete bipartite graph. The complexity of the case with k=3 colors is open. Variations and special ...

2009

Delaunay Graphs of Point Sets in the Plane With Respect to Axis-Parallel Rectangles

János Pach, Gábor Tardos

Given a point set P in the plane, the Delaunay graph with respect to axis-parallel rectangles is a graph defined on the vertex set P, whose two points p, q is an element of P are connected by an edge if and only if there is a rectangle parallel to the coor ...

Wiley-Blackwell2009

Drawing cubic graphs with at most five slopes

János Pach, Balázs Keszegh

We show that every graph G with maximum degree three has a straight-line drawing in the plane using edges of at most five different slopes. Moreover, if G is connected and has at least one vertex of degree less than three, then four directions suffice. ...

2008

Convexly independent subsets of the Minkowski sum of planar point sets

János Pach, Friedrich Eisenbrand, Thomas Rothvoss

Let P and Q be finite sets of points in the plane. In this note we consider the largest cardinality of a subset of the Minkowski sum S ⊆ P⊕Q which consist of convex independent points. We show that, if P and Q contain at most n points, then |S| = O(n^(4/3) ...

American Mathematical Society2008

Variations of coloring problems related to scheduling and discrete tomography

Bernard Ries

The graph coloring problem is one of the most famous problems in graph theory and has a large range of applications. It consists in coloring the vertices of an undirected graph with a given number of colors such that two adjacent vertices get different col ...

EPFL2007

Bicolored matchings in some classes of graphs

Dominique de Werra, Bernard Ries

We consider the problem of finding in a graph a set

R

of edges to be colored in red so that there are maximum matchings having some prescribed numbers of red edges. For regular bipartite graphs with

n

nodes on each side, we give sufficient conditions f ...

2007

Robust Routing for Dynamic Wireless Networks Based on Stable Embeddings

Matthias Grossglauser, Suhas Diggavi, Dominique Florian Tschopp, Jörg Widmer

Routing packets is a central function of multi-hop wireless networks. Traditionally, there have been two paradigms for routing, either based on the geographical coordinates of the nodes (geographic routing), or based on the connectivity graph (topology-bas ...

2007

Graph orientations with edge-connection and parity constraints

Parity (matching theory) and connectivity (network flows) are two main branches of combinatorial optimization. In an attempt to understand better their interrelation, we study a problem where both parity and connectivity requirements are imposed. The main ...

2001

Computing Vertex Connectivity: New Bounds from Old Techniques

Monika Henzinger

The vertex connectivity K of a graph is the smallest number of vertices whose deletion separates the graph or makes it trivial. We present the fastest known deterministic algorithm for finding the vertex connectivity and a corresponding separator. The time ...

2000

Bicolored matchings in some classes of graphs

Dominique de Werra, Bernard Ries

We consider the problem of finding in a graph a set

R

of edges to be colored in red so that there are maximum matchings having some prescribed numbers of red edges. For regular bipartite graphs with

n

nodes on each side, we give sufficient conditions f ...

2007