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Pursuit–evasion
Pursuit–evasion (variants of which are referred to as cops and robbers and graph searching) is a family of problems in mathematics and computer science in which one group attempts to track down members of another group in an environment. Early work on problems of this type modeled the environment geometrically. In 1976, Torrence Parsons introduced a formulation whereby movement is constrained by a graph. The geometric formulation is sometimes called continuous pursuit–evasion, and the graph formulation discrete pursuit–evasion (also called graph searching). Current research is typically limited to one of these two formulations. Discrete formulation In the discrete formulation of the pursuit–evasion problem, the environment is modeled as a graph. Problem definition There are innumerable possible variants of pursuit–evasion, though they tend to share many elements. A typical, basic example is as follows (cops and robber games): Pursuers and evaders occupy nodes of a g ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cop-win Graph
In graph theory, a cop-win graph is an undirected graph on which the pursuer (cop) can always win a pursuit–evasion game against a robber, with the players taking alternating turns in which they can chose to move along an edge of a graph or stay put, until the cop lands on the robber's vertex. Finite cop-win graphs are also called dismantlable graphs or constructible graphs, because they can be dismantled by repeatedly removing a dominated vertex (one whose closed neighborhood is a subset of another vertex's neighborhood) or constructed by repeatedly adding such a vertex. The cop-win graphs can be recognized in polynomial time by a greedy algorithm that constructs a dismantling order. They include the chordal graphs, and the graphs that contain a universal vertex. Definitions Pursuit–evasion Cop-win graphs can be defined by a pursuit–evasion game in which two players, a cop and a robber, are positioned at different initial vertices of a given undirected graph. The cop ch ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Haven (graph Theory)
In graph theory, a haven is a certain type of function on sets of vertices in an undirected graph. If a haven exists, it can be used by an evader to win a pursuit–evasion game on the graph, by consulting the function at each step of the game to determine a safe set of vertices to move into. Havens were first introduced by as a tool for characterizing the treewidth of graphs. Their other applications include proving the existence of small separators on minor-closed families of graphs, and characterizing the ends and clique minors of infinite graphs... Definition If is an undirected graph, and is a set of vertices, then an -flap is a nonempty connected component of the subgraph of formed by deleting . A haven of order in is a function that assigns an -flap to every set of fewer than vertices. This function must also satisfy additional constraints which are given differently by different authors. The number is called the ''order'' of the haven.. In the original defin ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chases And Escapes
''Chases and Escapes: The Mathematics of Pursuit and Evasion'' is a mathematics book on continuous pursuit–evasion problems. It was written by Paul J. Nahin, and published by the Princeton University Press in 2007. It was reissued as a paperback reprint in 2012. The Basic Library List Committee of the Mathematical Association of America has rated this book as essential for inclusion in undergraduate mathematics libraries. Topics The book has four chapters, covering the solutions to 21 continuous pursuit–evasion problems, with an additional 10 "challenge problems" left for readers to solve, with solutions given in an appendix. The problems are presented as entertaining stories that "breathe life into the mathematics and invite wider engagement", and their solutions use varied methods, including the computer calculation of numerical solutions for differential equations whose solutions have no closed form. Most of the material was previously known, but is collected here for the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Treewidth
In graph theory, the treewidth of an undirected graph is an integer number which specifies, informally, how far the graph is from being a tree. The smallest treewidth is 1; the graphs with treewidth 1 are exactly the trees and the forests. The graphs with treewidth at most 2 are the series–parallel graphs. The maximal graphs with treewidth exactly are called '' -trees'', and the graphs with treewidth at most are called '' partial -trees''. Many other well-studied graph families also have bounded treewidth. Treewidth may be formally defined in several equivalent ways: in terms of the size of the largest vertex set in a tree decomposition of the graph, in terms of the size of the largest clique in a chordal completion of the graph, in terms of the maximum order of a haven describing a strategy for a pursuit–evasion game on the graph, or in terms of the maximum order of a bramble, a collection of connected subgraphs that all touch each other. Treewidth is commonly used as a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Torrence Parsons
Torrence Douglas Parsons (1941–1987) was an American mathematician. He worked mainly in graph theory, and is known for introducing a graph-theoretic view of pursuit–evasion problems (Parsons 1976, 1978). He obtained his Ph.D. from Princeton University Princeton University is a private research university in Princeton, New Jersey. Founded in 1746 in Elizabeth as the College of New Jersey, Princeton is the fourth-oldest institution of higher education in the United States and one of the ... in 1966 under the supervision of Albert W. Tucker. Selected publications * * Notes Further reading Memorial articles in *''Journal of Graph Theory'' vol. 12 *''Discrete Mathematics'' vol. 78 1941 births 1987 deaths 20th-century American mathematicians Graph theorists Princeton University alumni {{US-mathematician-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Princess And Monster Game
In game theory, a princess and monster game is a pursuit–evasion game played by two players in a region. Formal Definition In his book ''Differential Games'' (1965), Rufus Isaacs defined the game as: This game remained a well-known open problem until it was solved by Shmuel Gal in the late 1970s. His optimal strategy for the princess is to move to a random location in the room and stay still for a time interval which is neither too short nor too long, before going to another (independent) random location and repeating the procedure. The proposed optimal search strategy for the monster is based on subdividing the room into many narrow rectangles, picking a rectangle at random and searching it in some specific way, after some time picking another rectangle randomly and independently, and so on. Princess and monster games can be played on a pre-selected graph. It can be demonstrated that for any finite graph an optimal mixed search strategy exists that results in a finit ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Scotland Yard (board Game)
''Scotland Yard'' is a board game in which a team of players controlling different detectives cooperate to track down a player controlling a criminal as they move around a board representing the streets of London. It was first published in 1983. It is named after Scotland Yard - the headquarters of London's Metropolitan Police Service in real-life. ''Scotland Yard'' is an asymmetric board game, during which the detective players cooperatively solve a variant of the pursuit–evasion problem. The game is published by Ravensburger in most of Europe and Canada and by Milton Bradley in the United States. It received the ''Spiel des Jahres'' (Game of the Year) award in 1983 - the same year that it was published. Gameplay One player controls 'Mr. X': a criminal whose location is only revealed periodically throughout gameplay. The other players each control a detective, all of which are always present on the board. All players start with a number of tokens ("tickets") which each allow ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Rufus Isaacs (game Theorist)
Rufus Philip Isaacs (June 11, 1914 – January 18, 1981) was a game theorist especially prominent in the 1950s and 1960s with his work on differential games. Biography Isaacs was born on 11 June 1914 in New York City. He worked for the RAND Corporation from 1948 until winter 1954/1955. His investigation stemmed from classic pursuit–evasion type zero-sum dynamic two-player games such as the Princess and monster game. In 1942, he married Rose Bicov, and they had two daughters. His work in pure mathematics included working with monodiffric functions, fractional-order mappings, graph theory, analytic functions, and number theory. In graph theory he constructed the first two infinite families of snarks. In applied mathematics, he worked with aerodynamics, elasticity, optimization, and differential games, which he is most known for. He received his bachelor's degree from MIT in 1936, and received his MA and PhD from Columbia University in 1942 and 1943 respectively. His fir ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pathwidth
In graph theory, a path decomposition of a graph is, informally, a representation of as a "thickened" path graph, and the pathwidth of is a number that measures how much the path was thickened to form . More formally, a path-decomposition is a sequence of subsets of vertices of such that the endpoints of each edge appear in one of the subsets and such that each vertex appears in a contiguous subsequence of the subsets,. and the pathwidth is one less than the size of the largest set in such a decomposition. Pathwidth is also known as interval thickness (one less than the maximum clique size in an interval supergraph of ), vertex separation number, or node searching number. Pathwidth and path-decompositions are closely analogous to treewidth and tree decompositions. They play a key role in the theory of graph minors: the families of graphs that are closed under graph minors and do not include all forests may be characterized as having bounded pathwidth, and the "vortice ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mathematics
Mathematics is an area of knowledge that includes the topics of numbers, formulas and related structures, shapes and the spaces in which they are contained, and quantities and their changes. These topics are represented in modern mathematics with the major subdisciplines of number theory, algebra, geometry, and analysis, respectively. There is no general consensus among mathematicians about a common definition for their academic discipline. Most mathematical activity involves the discovery of properties of abstract objects and the use of pure reason to prove them. These objects consist of either abstractions from nature orin modern mathematicsentities that are stipulated to have certain properties, called axioms. A ''proof'' consists of a succession of applications of deductive rules to already established results. These results include previously proved theorems, axioms, andin case of abstraction from naturesome basic properties that are considered true starting points of t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Missile Guidance
Missile guidance refers to a variety of methods of guiding a missile or a guided bomb to its intended target. The missile's target accuracy is a critical factor for its effectiveness. Guidance systems improve missile accuracy by improving its Probability of Guidance (Pg). These guidance technologies can generally be divided up into a number of categories, with the broadest categories being "active", "passive", and "preset" guidance. Missiles and guided bombs generally use similar types of guidance system, the difference between the two being that missiles are powered by an onboard engine, whereas guided bombs rely on the speed and height of the launch aircraft for propulsion. History The concept of unmanned guidance originated at least as early as World War I, with the idea of remotely guiding an airplane bomb onto a target, such as the systems developed for the first powered drones by Archibald Low (The Father of Radio Guidance). In World War II, guided missiles were first d ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Angel Problem
The angel problem is a question in combinatorial game theory proposed by John Horton Conway. The game is commonly referred to as the Angels and Devils game.John H. Conway, The angel problem', in: Richard Nowakowski (editor) ''Games of No Chance'', volume 29 of MSRI Publications, pages 3–12, 1996. The game is played by two player (game), players called the angel and the devil. It is played on an infinite chessboard (or equivalently the points of a 2D lattice (group), lattice). The angel has a power ''k'' (a natural number 1 or higher), specified before the game starts. The board starts empty with the angel in one square. On each turn, the angel jumps to a different empty square which could be reached by at most ''k'' moves of a King (chess), chess king, i.e. the distance from the starting square is at most ''k'' in the Chebyshev distance, infinity norm. The devil, on its turn, may add a block on any single square not containing the angel. The angel may leap over blocked squares ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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