13,576 research outputs found
Dynamic Geometric Set Cover and Hitting Set
We investigate dynamic versions of geometric set cover and hitting set where
points and ranges may be inserted or deleted, and we want to efficiently
maintain an (approximately) optimal solution for the current problem instance.
While their static versions have been extensively studied in the past,
surprisingly little is known about dynamic geometric set cover and hitting set.
For instance, even for the most basic case of one-dimensional interval set
cover and hitting set, no nontrivial results were known. The main contribution
of our paper are two frameworks that lead to efficient data structures for
dynamically maintaining set covers and hitting sets in and
. The first framework uses bootstrapping and gives a
-approximate data structure for dynamic interval set cover in
with amortized update time for any
constant ; in , this method gives -approximate
data structures for unit-square (and quadrant) set cover and hitting set with
amortized update time. The second framework uses local
modification, and leads to a -approximate data structure for
dynamic interval hitting set in with
amortized update time; in , it
gives -approximate data structures for unit-square (and quadrant) set
cover and hitting set in the \textit{partially} dynamic settings with
amortized update time.Comment: A preliminary version will appear in SoCG'2
Stabbing line segments with disks: complexity and approximation algorithms
Computational complexity and approximation algorithms are reported for a
problem of stabbing a set of straight line segments with the least cardinality
set of disks of fixed radii where the set of segments forms a straight
line drawing of a planar graph without edge crossings. Close
geometric problems arise in network security applications. We give strong
NP-hardness of the problem for edge sets of Delaunay triangulations, Gabriel
graphs and other subgraphs (which are often used in network design) for and some constant where and
are Euclidean lengths of the longest and shortest graph edges
respectively. Fast -time -approximation algorithm is
proposed within the class of straight line drawings of planar graphs for which
the inequality holds uniformly for some constant
i.e. when lengths of edges of are uniformly bounded from above by
some linear function of Comment: 12 pages, 1 appendix, 15 bibliography items, 6th International
Conference on Analysis of Images, Social Networks and Texts (AIST-2017
Bidimensionality and Geometric Graphs
In this paper we use several of the key ideas from Bidimensionality to give a
new generic approach to design EPTASs and subexponential time parameterized
algorithms for problems on classes of graphs which are not minor closed, but
instead exhibit a geometric structure. In particular we present EPTASs and
subexponential time parameterized algorithms for Feedback Vertex Set, Vertex
Cover, Connected Vertex Cover, Diamond Hitting Set, on map graphs and unit disk
graphs, and for Cycle Packing and Minimum-Vertex Feedback Edge Set on unit disk
graphs. Our results are based on the recent decomposition theorems proved by
Fomin et al [SODA 2011], and our algorithms work directly on the input graph.
Thus it is not necessary to compute the geometric representations of the input
graph. To the best of our knowledge, these results are previously unknown, with
the exception of the EPTAS and a subexponential time parameterized algorithm on
unit disk graphs for Vertex Cover, which were obtained by Marx [ESA 2005] and
Alber and Fiala [J. Algorithms 2004], respectively.
We proceed to show that our approach can not be extended in its full
generality to more general classes of geometric graphs, such as intersection
graphs of unit balls in R^d, d >= 3. Specifically we prove that Feedback Vertex
Set on unit-ball graphs in R^3 neither admits PTASs unless P=NP, nor
subexponential time algorithms unless the Exponential Time Hypothesis fails.
Additionally, we show that the decomposition theorems which our approach is
based on fail for disk graphs and that therefore any extension of our results
to disk graphs would require new algorithmic ideas. On the other hand, we prove
that our EPTASs and subexponential time algorithms for Vertex Cover and
Connected Vertex Cover carry over both to disk graphs and to unit-ball graphs
in R^d for every fixed d
A decomposition technique for pursuit evasion games with many pursuers
Here we present a decomposition technique for a class of differential games.
The technique consists in a decomposition of the target set which produces, for
geometrical reasons, a decomposition in the dimensionality of the problem.
Using some elements of Hamilton-Jacobi equations theory, we find a relation
between the regularity of the solution and the possibility to decompose the
problem. We use this technique to solve a pursuit evasion game with multiple
agents
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