4,348 research outputs found
The Power of Dynamic Distance Oracles: Efficient Dynamic Algorithms for the Steiner Tree
In this paper we study the Steiner tree problem over a dynamic set of
terminals. We consider the model where we are given an -vertex graph
with positive real edge weights, and our goal is to maintain a tree
which is a good approximation of the minimum Steiner tree spanning a terminal
set , which changes over time. The changes applied to the
terminal set are either terminal additions (incremental scenario), terminal
removals (decremental scenario), or both (fully dynamic scenario). Our task
here is twofold. We want to support updates in sublinear time, and keep
the approximation factor of the algorithm as small as possible. We show that we
can maintain a -approximate Steiner tree of a general graph in
time per terminal addition or removal. Here,
denotes the stretch of the metric induced by . For planar graphs we achieve
the same running time and the approximation ratio of .
Moreover, we show faster algorithms for incremental and decremental scenarios.
Finally, we show that if we allow higher approximation ratio, even more
efficient algorithms are possible. In particular we show a polylogarithmic time
-approximate algorithm for planar graphs.
One of the main building blocks of our algorithms are dynamic distance
oracles for vertex-labeled graphs, which are of independent interest. We also
improve and use the online algorithms for the Steiner tree problem.Comment: Full version of the paper accepted to STOC'1
Optimal Path Planning in Distinct Topo-Geometric Classes using Neighborhood-augmented Graph and its Application to Path Planning for a Tethered Robot in 3D
Many robotics applications benefit from being able to compute multiple
locally optimal paths in a given configuration space. Examples include path
planning for of tethered robots with cable-length constraints, systems
involving cables, multi-robot topological exploration & coverage, and,
congestion reduction for mobile robots navigation without inter-robot
coordination. Existing paradigm is to use topological path planning methods
that can provide optimal paths from distinct topological classes available in
the underlying configuration space. However, these methods usually require
non-trivial and non-universal geometrical constructions, which are
prohibitively complex or expensive in 3 or higher dimensional configuration
spaces with complex topology. Furthermore, topological methods are unable to
distinguish between locally optimal paths that belong to the same topological
class but are distinct because of genus-zero obstacles in 3D or due to
high-cost or high-curvature regions. In this paper we propose an universal and
generalized approach to multi-class path planning using the concept of a novel
neighborhood-augmented graph, search-based planning in which can compute paths
in distinct topo-geometric classes. This approach can find desired number of
locally optimal paths in a wider variety of configuration spaces without
requiring any complex pre-processing or geometric constructions. Unlike the
existing topological methods, resulting optimal paths are not restricted to
distinct topological classes, thus making the algorithm applicable to many
other problems where locally optimal and geometrically distinct paths are of
interest. For the demonstration of an application of the proposed approach, we
implement our algorithm to planning for shortest traversible paths for a
tethered robot with cable-length constraint navigating in 3D and validate it in
simulations & experiments.Comment: 18 pages, 17 figure
An Overview of Mobile Ad Hoc Networks for the Existing Protocols and Applications
Mobile Ad Hoc Network (MANET) is a collection of two or more devices or nodes
or terminals with wireless communications and networking capability that
communicate with each other without the aid of any centralized administrator
also the wireless nodes that can dynamically form a network to exchange
information without using any existing fixed network infrastructure. And it's
an autonomous system in which mobile hosts connected by wireless links are free
to be dynamically and some time act as routers at the same time, and we discuss
in this paper the distinct characteristics of traditional wired networks,
including network configuration may change at any time, there is no direction
or limit the movement and so on, and thus needed a new optional path Agreement
(Routing Protocol) to identify nodes for these actions communicate with each
other path, An ideal choice way the agreement should not only be able to find
the right path, and the Ad Hoc Network must be able to adapt to changing
network of this type at any time. and we talk in details in this paper all the
information of Mobile Ad Hoc Network which include the History of ad hoc,
wireless ad hoc, wireless mobile approaches and types of mobile ad Hoc
networks, and then we present more than 13 types of the routing Ad Hoc Networks
protocols have been proposed. In this paper, the more representative of routing
protocols, analysis of individual characteristics and advantages and
disadvantages to collate and compare, and present the all applications or the
Possible Service of Ad Hoc Networks.Comment: 24 Pages, JGraph-Hoc Journa
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