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A GAME OF COPS AND ROBBERS
, 1984
"... Let G be a finite connected graph. Two players, called cop C and robber R, play a game on G according to the following rules. First C then R occupy some vertex of G. After that they move alternately along edges of G. The cop C wins if he succeeds in putting himself on top of the robber R, otherwise ..."
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Cited by 121 (0 self)
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Let G be a finite connected graph. Two players, called cop C and robber R, play a game on G according to the following rules. First C then R occupy some vertex of G. After that they move alternately along edges of G. The cop C wins if he succeeds in putting himself on top of the robber R, otherwise R wins. We review an algorithmic characterization and structural description due to Nowakowski and Winkler. Then we consider the general situation where n cops chase the robber. It is shown that there are graphs on which arbitrarily many cops are needed to catch the robber. In contrast to this result, we prove that for planar graphs 3 cops always suffice to win.
VisibilityBased PursuitEvasion in a Polygonal Environment
 International Journal of Computational Geometry and Applications
, 1997
"... This paper addresses the problem of planning the motion of one or more pursuers in a polygonal environment to eventually "see" an evader that is unpredictable, has unknown initial position, and is capable of moving arbitrarily fast. This problem was first introduced by Suzuki and Yamashita ..."
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Cited by 109 (25 self)
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This paper addresses the problem of planning the motion of one or more pursuers in a polygonal environment to eventually "see" an evader that is unpredictable, has unknown initial position, and is capable of moving arbitrarily fast. This problem was first introduced by Suzuki and Yamashita. Our study of this problem is motivated in part by robotics applications, such as surveillance with a mobile robot equipped with a camera that must find a moving target in a cluttered workspace. A few bounds are introduced, and a complete algorithm is presented for computing a successful motion strategy for a single pursuer. For simplyconnected free spaces, it is shown that the minimum number of pursuers required is \Theta(lg n). For multiplyconnected free spaces, the bound is \Theta( p h + lg n) pursuers for a polygon that has n edges and h holes. A set of problems that are solvable by a single pursuer and require a linear number of recontaminations is shown. The complete algorithm searches a f...
Distributed control applications within sensor networks
 IEEE PROCEEDINGS SPECIAL ISSUE ON DISTRIBUTED SENSOR NETWORKS
, 2003
"... Sensor networks are gaining a central role in the research community. This paper addresses some of the issues arising from the use of sensor networks in control applications. Classical control theory proves to be insufficient in modeling distributed control problems where issues of communication del ..."
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Cited by 101 (27 self)
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Sensor networks are gaining a central role in the research community. This paper addresses some of the issues arising from the use of sensor networks in control applications. Classical control theory proves to be insufficient in modeling distributed control problems where issues of communication delay, jitter, and time synchronization between components are not negligible. After discussing our hardware and software platform and our target application, we review useful models of computation and then suggest a mixed model for design, analysis, and synthesis of control algorithms within sensor networks. We present a hierarchical model composed of continuous timetrigger components at the low level and discrete eventtriggered components at the high level.
SEARCHING AND PEBBLING
, 1986
"... We relate the search number of an undirected graph G with the minimum and maximum of the progressive pebble demands of the directed acyclic graphs obtained by orienting (7. Towards this end, we introduce nodesearching, a slight variant of searching, in which an edge is cleared by placing searchers ..."
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Cited by 94 (1 self)
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We relate the search number of an undirected graph G with the minimum and maximum of the progressive pebble demands of the directed acyclic graphs obtained by orienting (7. Towards this end, we introduce nodesearching, a slight variant of searching, in which an edge is cleared by placing searchers on both of its endpoints. We also show that the minimum number of searchers necessary to nodesearch a graph equals its vertex separator plus one. Key words. Searching a graph, pebble games, layout parameters of a graph, vertex separator of a graph.
Visibilitybased pursuitevasion with limited field of view.
 The International Journal of Robotics Research,
, 2006
"... Abstract We study a form of the pursuitevasion problem, in which one or more searchers must move through a given environment so as to guarantee detection of any and all evaders, which can move arbitrarily fast. Our goal is to develop techniques for coordinating teams of robots to execute this task ..."
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Cited by 92 (1 self)
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Abstract We study a form of the pursuitevasion problem, in which one or more searchers must move through a given environment so as to guarantee detection of any and all evaders, which can move arbitrarily fast. Our goal is to develop techniques for coordinating teams of robots to execute this task in application domains such as clearing a building, for reasons of security or safety. To this end, we introduce a new class of searcher, the φsearcher, which can be readily instantiated as a physical mobile robot. We present a detailed analysis of the pursuitevasion problem using φsearchers. We show that computing the minimum number of φsearchers required to search a given environment is NPhard, and present the first complete search algorithm for a single φsearcher. We show how this algorithm can be extended to handle multiple searchers, and give examples of computed trajectories.
A VisibilityBased PursuitEvasion Problem
 SUBMITTED TO THE INTERNATIONAL JOURNAL OF COMPUTATIONAL GEOMETRY AND APPLICATIONS
"... This paper addresses the problem of planning the motion of one or more pursuers in a polygonal environment to eventually "see" an evader that is unpredictable, has unknown initial position, and is capable of moving arbitrarily fast. A visibility region is associated witheach pursuer, and t ..."
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Cited by 82 (1 self)
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This paper addresses the problem of planning the motion of one or more pursuers in a polygonal environment to eventually "see" an evader that is unpredictable, has unknown initial position, and is capable of moving arbitrarily fast. A visibility region is associated witheach pursuer, and the goal is to guarantee that the evader will ultimately lie in at least one visibility region. The study of this problem is motivated inpart by robotics applications, such as surveillance with a mobile robot equipped withacamera that must nd a moving target in a cluttered workspace. A few bounds are introduced, and a complete algorithm is presented for computing a successful motion strategy. For a simplyconnected free space, a logarithmic bound is established on the minimum of pursuers needed. Loose bounds for multiplyconnected free spaces are also given. A set of problems that are solvable by a single pursuer and require a linear number of recontaminations is shown. The complete algorithm searches a nite cell complex that is constructed onthebasis of critical information changes. This concept can be applied in principle to multiplepursuer problems, and the case of a single pursuer has been implemented. Several solution strategies are shown, most of which were computed in a few seconds on a standard workstation.
Finding an Unpredictable Target in a Workspace with Obstacles
, 1997
"... This paper introduces a visibilitybased motion planning problem in which the task is to coordinate the motions of one or more robots that have omnidirectional vision sensors, to eventually "see" a target that is unpredictable, has unknown initial position, and is capable of moving arbitra ..."
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Cited by 79 (13 self)
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This paper introduces a visibilitybased motion planning problem in which the task is to coordinate the motions of one or more robots that have omnidirectional vision sensors, to eventually "see" a target that is unpredictable, has unknown initial position, and is capable of moving arbitrarily fast. A visibility region is associated with each robot, and the goal is to guarantee that the target will ultimately lie in at least one visibility region. Both a formal characterization of the general problem and several interesting problem instances are presented. A complete algorithm for computing the motion strategy of the robots is also presented, and is based on searching a finite cell complex that is constructed on the basis of critical information changes. A few computed solution strategies are shown. Several bounds on the minimum number of needed robots are also discussed. 1 Introduction Have you ever searched for someone in a building, possibly exploring the same places multiple time...
Directed TreeWidth
, 1998
"... We generalize the concept of treewidth to directed graphs, and prove that every directed graph with no "haven" of large order has small treewidth. Conversely, a digraph with a large haven has large treewidth. We also show that the Hamilton cycle problem and other NPhard problems can be ..."
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Cited by 57 (2 self)
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We generalize the concept of treewidth to directed graphs, and prove that every directed graph with no "haven" of large order has small treewidth. Conversely, a digraph with a large haven has large treewidth. We also show that the Hamilton cycle problem and other NPhard problems can be solved in polynomial time when restricted to digraphs of bounded treewidth.
VisibilityBased PursuitEvasion in a Polygonal Region by a Searcher
 Proceedings of the International Colloquium on Automata, Languages and Programming (ICALP
, 2001
"... We consider the most basic visibilitybased pursuitevasion problem defined as follows: Given a polygonal region, a searcher with 360 # vision, and an unpredictable intruder that is arbitrarily faster than the searcher, plan the motion of the searcher so as to see the intruder. In this paper, we ..."
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Cited by 47 (1 self)
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We consider the most basic visibilitybased pursuitevasion problem defined as follows: Given a polygonal region, a searcher with 360 # vision, and an unpredictable intruder that is arbitrarily faster than the searcher, plan the motion of the searcher so as to see the intruder. In this paper, we present simple necessary and su#cient conditions for a polygon to be searchable, which settles a decadeold open problem raised in [15]. We also show that every searchable polygon is also searchable by a searcher with two flashlights (that is, ray visions). This implies, combined with the previous work, that there is an O(n 2 )time algorithm for constructing a search path for an nsided polygon. 1 Introduction The visibilitybased pursuitevasion problem is that of planning the motion of one or more searchers in a polygonal environment to eventually see an intruder that is unpredictable, has unknown initial position, and is capable of moving arbitrarily fast. This problem can mode...