378 research outputs found
Distributed Dominating Set Approximations beyond Planar Graphs
The Minimum Dominating Set (MDS) problem is one of the most fundamental and
challenging problems in distributed computing. While it is well-known that
minimum dominating sets cannot be approximated locally on general graphs, over
the last years, there has been much progress on computing local approximations
on sparse graphs, and in particular planar graphs.
In this paper we study distributed and deterministic MDS approximation
algorithms for graph classes beyond planar graphs. In particular, we show that
existing approximation bounds for planar graphs can be lifted to bounded genus
graphs, and present (1) a local constant-time, constant-factor MDS
approximation algorithm and (2) a local -time
approximation scheme. Our main technical contribution is a new analysis of a
slightly modified variant of an existing algorithm by Lenzen et al.
Interestingly, unlike existing proofs for planar graphs, our analysis does not
rely on direct topological arguments.Comment: arXiv admin note: substantial text overlap with arXiv:1602.0299
The Generalised Colouring Numbers on Classes of Bounded Expansion
The generalised colouring numbers , ,
and were introduced by Kierstead and Yang as
generalisations of the usual colouring number, also known as the degeneracy of
a graph, and have since then found important applications in the theory of
bounded expansion and nowhere dense classes of graphs, introduced by
Ne\v{s}et\v{r}il and Ossona de Mendez. In this paper, we study the relation of
the colouring numbers with two other measures that characterise nowhere dense
classes of graphs, namely with uniform quasi-wideness, studied first by Dawar
et al. in the context of preservation theorems for first-order logic, and with
the splitter game, introduced by Grohe et al. We show that every graph
excluding a fixed topological minor admits a universal order, that is, one
order witnessing that the colouring numbers are small for every value of .
Finally, we use our construction of such orders to give a new proof of a result
of Eickmeyer and Kawarabayashi, showing that the model-checking problem for
successor-invariant first-order formulas is fixed-parameter tractable on
classes of graphs with excluded topological minors
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