|
Dense Subgraph
In graph theory and computer science, a dense subgraph is a subgraph with many edges per vertex. This is formalized as follows: let be an undirected graph and let be a subgraph of . Then the ''density'' of is defined to be: :d(S) = The density of the maximally dense subgraph of a graph is sometimes referred to as its subgraph density. A subgraph with maximal density can also be seen as a subgraph with maximal average degree in the graph. Subgraph density is asymptotic to the related notion of arboricity and to graph degeneracy. Densest subgraph The densest subgraph problem is that of finding a subgraph of maximum density. In 1984, Andrew V. Goldberg developed a polynomial time algorithm to find the maximum density subgraph using a max flow technique. This has been improved by Gallo, Grigoriadis and Tarjan in 1989 to run in time. A simple LP for finding the optimal solution was given by Charikar in 2000. Many of the exact algorithms for solving the densest subgraph pr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Exponential Time Hypothesis
In computational complexity theory, the exponential time hypothesis is an unproven computational hardness assumption that was formulated by . It states that satisfiability of 3-CNF Boolean formulas cannot be solved in subexponential time, 2^. More precisely, the usual form of the hypothesis asserts the existence of a number s_3 > 0 such that all algorithms that correctly solve this problem require time at least 2^. The exponential time hypothesis, if true, would imply that P ≠NP, but it is a stronger statement. It implies that many computational problems are equivalent in complexity, in the sense that if one of them has a subexponential time algorithm then they all do, and that many known algorithms for these problems have optimal or near-optimal time Definition The problem is a version of the Boolean satisfiability problem in which the input to the problem is a Boolean expression in conjunctive normal form (that is, an ''and'' of ''ors'' of variables and their negations) wi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Unique Games Conjecture
In computational complexity theory, the unique games conjecture (often referred to as UGC) is a conjecture made by Subhash Khot in 2002. The conjecture postulates that the problem of determining the approximate ''value'' of a certain type of game, known as a ''unique game'', has NP-hard computational complexity. It has broad applications in the theory of hardness of approximation. If the unique games conjecture is true and P ≠NP,The unique games conjecture is vacuously true if P = NP, as then every problem in NP would also be NP-hard. then for many important problems it is not only impossible to get an exact solution in polynomial time (as postulated by the P versus NP problem), but also impossible to get a good polynomial-time approximation. The problems for which such an inapproximability result would hold include constraint satisfaction problems, which crop up in a wide variety of disciplines. The conjecture is unusual in that the academic world ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Small Set Expansion Hypothesis
The small set expansion hypothesis or small set expansion conjecture in computational complexity theory is an unproven computational hardness assumption. Under the small set expansion hypothesis it is assumed to be computationally infeasible to distinguish between a certain class of expander graphs called "small set expanders" and other graphs that are very far from being small set expanders. This assumption implies the hardness of several other computational problems, and the optimality of certain known approximation algorithms. The small set expansion hypothesis is related to the unique games conjecture, another unproven computational hardness assumption according to which accurately approximating the value of certain games is computationally infeasible. If the small set expansion hypothesis is true, then so is the unique games conjecture. Background The ''edge expansion'' of a set X of vertices in a graph G is defined as \frac, where the vertical bars denote the number of el ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Barna Saha
Barna Saha is an Indian-American theoretical computer scientist whose research interests include algorithmic applications of the probabilistic method, probabilistic databases, fine-grained complexity, and the analysis of big data. She is an associate professor and Jacobs Faculty Scholar in the Department of Computer Science & Engineering at the University of California, San Diego. Education and career Saha is originally from Siliguri, and grew up intending to follow her mother into a career in chemistry. She was an undergraduate at Jadavpur University, and earned a master's degree at IIT Kanpur in 2006. She completed her Ph.D. in 2011 at the University of Maryland, College Park, with Samir Khuller as her doctoral advisor. Her dissertation was ''Approximation Algorithms for Resource Allocation''. After completing her doctorate, she became a senior member of the technical research staff at the Shannon Research Laboratory of AT&T Labs. In 2014 she moved to the College of Informati ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Samir Khuller
Samir Khuller (born 1965) is a professor of Computer Science and the Peter and Adrienne Barris Chair of Computer Science at Northwestern University. He was previously Professor and Elizabeth Stevinson Iribe Chair of Computer Science in the University of Maryland's Department of Computer Science. His research is in the area of algorithm design, specifically on combinatorial optimization, graphs and networks and scheduling. Biography Khuller obtained his undergraduate degree from the Indian Institute of Technology Kanpur and was awarded a PhD in 1990 from Cornell University as a student of Vijay Vazirani. From 1990 to 1992, he was a research associate at UMIACS (the Institute for Advanced Computer Studies), a division of the University of Maryland. In 1992 he joined the faculty of the University of Maryland Department of Computer Science. He became the Elizabeth Stevinson Iribe Chair of Computer Science at the Department of Computer Science in 2012, a position he held until 2017. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Planar Graph
In graph theory, a planar graph is a graph (discrete mathematics), graph that can be graph embedding, embedded in the plane (geometry), plane, i.e., it can be drawn on the plane in such a way that its edges intersect only at their endpoints. In other words, it can be drawn in such a way that no edges cross each other. Such a drawing is called a plane graph, or a planar embedding of the graph. A plane graph can be defined as a planar graph with a mapping from every node to a point on a plane, and from every edge to a plane curve on that plane, such that the extreme points of each curve are the points mapped from its end nodes, and all curves are disjoint except on their extreme points. Every graph that can be drawn on a plane can be drawn on the sphere as well, and vice versa, by means of stereographic projection. Plane graphs can be encoded by combinatorial maps or rotation systems. An equivalence class of topologically equivalent drawings on the sphere, usually with addit ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Interval Graph
In graph theory, an interval graph is an undirected graph formed from a set of intervals on the real line, with a vertex for each interval and an edge between vertices whose intervals intersect. It is the intersection graph of the intervals. Interval graphs are chordal graphs and perfect graphs. They can be recognized in linear time, and an optimal graph coloring or maximum clique in these graphs can be found in linear time. The interval graphs include all proper interval graphs, graphs defined in the same way from a set of unit intervals. These graphs have been used to model food webs, and to study scheduling problems in which one must select a subset of tasks to be performed at non-overlapping times. Other applications include assembling contiguous subsequences in DNA mapping, and temporal reasoning. Definition An interval graph is an undirected graph formed from a family of intervals :S_i,\quad i=0,1,2,\dots by creating one vertex for each interval , and connecting two v ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Discrete Applied Mathematics
''Discrete Applied Mathematics'' is a peer-reviewed scientific journal covering algorithmic and applied areas of discrete mathematics. It is published by Elsevier and the editor-in-chief is Endre Boros (Rutgers University). The journal was split off from another Elsevier journal, ''Discrete Mathematics'', in 1979, with that journal's founder Peter Ladislaw Hammer as its founding editor-in-chief. Abstracting and indexing The journal is abstracted and indexing in: According to the ''Journal Citation Reports'', the journal has a 2020 impact factor The impact factor (IF) or journal impact factor (JIF) of an academic journal is a type of journal ranking. Journals with higher impact factor values are considered more prestigious or important within their field. The Impact Factor of a journa ... of 1.139. References External links *{{official website, http://www.journals.elsevier.com/discrete-applied-mathematics/ Discrete mathematics journals Academic journals established in ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Split Graph
In graph theory, a branch of mathematics, a split graph is a graph in which the vertices can be partitioned into a clique and an independent set. Split graphs were first studied by , and independently introduced by , where they called these graphs "polar graphs" (). A split graph may have more than one partition into a clique and an independent set; for instance, the path is a split graph, the vertices of which can be partitioned in three different ways: #the clique and the independent set #the clique and the independent set #the clique and the independent set Split graphs can be characterized in terms of their forbidden induced subgraphs: a graph is split if and only if no induced subgraph is a cycle on four or five vertices, or a pair of disjoint edges (the complement of a 4-cycle). Relation to other graph families From the definition, split graphs are clearly closed under complementation. Another characterization of split graphs involves complementation: they a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tree (graph Theory)
In graph theory, a tree is an undirected graph in which any two vertices are connected by path, or equivalently a connected acyclic undirected graph. A forest is an undirected graph in which any two vertices are connected by path, or equivalently an acyclic undirected graph, or equivalently a disjoint union of trees. A directed tree, oriented tree,See .See . polytree,See . or singly connected networkSee . is a directed acyclic graph (DAG) whose underlying undirected graph is a tree. A polyforest (or directed forest or oriented forest) is a directed acyclic graph whose underlying undirected graph is a forest. The various kinds of data structures referred to as trees in computer science have underlying graphs that are trees in graph theory, although such data structures are generally rooted trees. A rooted tree may be directed, called a directed rooted tree, either making all its edges point away from the root—in which case it is called an arborescence or out-tree†... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
