Cover-Decomposition and Polychromatic Numbers
@inproceedings{Bollobs2013CoverDecompositionAP, title={Cover-Decomposition and Polychromatic Numbers}, author={B{\'e}la Bollob{\'a}s and David Pritchard and Thomas Rothvoss and Alex D. Scott}, booktitle={SIAM J. Discret. Math.}, year={2013} }
A colouring of a hypergraph's vertices is polychromatic if every hyperedge contains at least one vertex of each colour; the polychromatic number is the maximum number of colours in such a colouring. Its dual, the cover-decomposition number, is the maximum number of disjoint hyperedge-covers. In geometric settings, there is extensive work on lower-bounding these numbers in terms of their trivial upper bounds (minimum hyperedge size & degree). Our goal is to get good lower bounds in natural…
15 Citations
Colouring Non-Even Digraphs
- MathematicsArXiv
- 2019
It is shown that every non-even digraph has dichromatic number at most 2 and an optimal colouring can be found in polynomial time and strengthens a previously known NP-hardness result by showing that deciding whether a directed graph is 2-colourable remains NP- hard even if it contains a feedback vertex set of bounded size.
Polychromatic colorings of hypergraphs with high balance
- Mathematics
- 2020
Let $m$ be a positive integer and $C = \{1,2,\dots,m\}$ be a set of $m$ colors. A polychromatic $m$-coloring of a hypergraph is a coloring of its vertices in such a way that every hyperedge contains…
Polychromatic colorings of complete graphs with respect to 1‐, 2‐factors and Hamiltonian cycles
- MathematicsJ. Graph Theory
- 2018
The H-polychromatic number of G, denoted poly_H(G), is the largest number of colors such that G has an H- polychromatic coloring.
Approximate Hypergraph Coloring under Low-discrepancy and Related Promises
- MathematicsAPPROX-RANDOM
- 2015
The complexity of approximate hypergraph coloring is studied, for both the maximization and minimization versions, when the input hypergraph is promised to have the following stronger properties than $2$-colorability: Rainbow colorability, low-discrepancy, and NP-hardness.
Hardness of Rainbow Coloring Hypergraphs
- MathematicsFSTTCS
- 2017
It is shown that for any Q,k >= 2 and \ell <= k/2, given a Qk-uniform hypergraph which admits a k-rainbow coloring satisfying k colors, it is NP-hard to compute an independent set of (1 - (\ell+1)/k + \eps)-fraction of vertices, for any constant \eps > 0.
Indecomposable coverings with unit discs
- MathematicsArXiv
- 2013
We disprove the 1980 conjecture of Janos Pach about the cover-decomposability of open convex sets by showing that the unit disc is not cover-decomposable. In fact, our proof easily generalizes to any…
Unsplittable Coverings in the Plane
- MathematicsWG
- 2015
A general coloring theorem for hypergraphs of a special type: {\em shift-chains} is proved, which shows that there is a constant $c>0$ such that, for any positive integer $m$, every $m$-fold covering of a region with unit disks splits into two coverings.
References
SHOWING 1-10 OF 68 REFERENCES
Polychromatic colorings of plane graphs
- MathematicsSCG '08
- 2008
AbstractWe show that the vertices of any plane graph in which every face is incident to at least g vertices can be colored by ⌊(3g−5)/4⌋ colors so that every color appears in every face. This is…
Problems and Results on 3-chromatic Hypergraphs and Some Related Questions
- Mathematics
A hypergraphi is a collection of sets. This paper deals with finite hy-pergraphs only. The sets in the hypergraph are called edges, the elements of these edges are points. The degree of a point is…
Semi-Strong Coloring of Intersecting Hypergraphs
- Mathematics
- 2012
For any c >= 2, a c-strong coloring of the hypergraph G is an assignment of colors to the vertices of G such that for every edge e of G, the vertices of e are colored by at least min{c,|e|} distinct…
Approximating the domatic number
- Mathematics, Computer ScienceSTOC '00
- 2000
D domatic number is made the first natural maximization problem (known to the authors) that is provably approximable to within polylogarithmic factors but no better.
Weak Conflict-Free Colorings of Point Sets and Simple Regions
- Mathematics, Computer ScienceCCCG
- 2007
This paper considers the weak conflict-free colorings of regions and points and gives efficient algorithms for coloring with the needed number of colors for axis-parallel rectangles.
Decomposition of Geometric Set Systems and Graphs
- MathematicsArXiv
- 2010
A detailed survey of all results on the cover-decomposability of polygons and the planar slope number, defined only for planar graphs as the smallest number s with the property that the graph has a straight-line drawing in the plane without any crossings such that the edges are segments of only s distinct slopes.
Delaunay graphs of point sets in the plane with respect to axis-parallel rectangles
- Computer Science, Mathematics
- 2009
This paper proves that the largest independent set in a randomly and uniformly selected point set in the unit square is O(n log(2) log n/ log n), with probability tending to 1.
Decomposing k-ARc-Strong Tournaments Into Strong Spanning Subdigraphs
- MathematicsComb.
- 2004
This paper conjecture that every k-arc-strong tournament contains k arc-disjoint spanning strong subdigraphs is formed, which solves a conjecture of Bang-Jensen and Gutin.
On 2-Coverings and 2-Packings of Laminar Families
- MathematicsESA
- 1999
The results imply approximation algorithms for some NP-hard problems in connectivity augmentation and related topics, based on efficient algorithms for finding appropriate colorings of the edges in a k-cover or a 2-packing, respectively, and they extend to the case where the edges have nonnegative weights.