The crossing number of a graph is a classic concept in graph theory that refers to the minimum number of edge crossings in a drawing of the graph in the plane. When a graph is drawn on a two-dimensional surface (like a piece of paper), edges can sometimes cross over each other. The goal is to find a layout of the graph that minimizes these crossings. Here's a more detailed explanation: 1. **Graph**: A graph consists of vertices (or nodes) connected by edges (or links).
The crossing number inequality is a concept from graph theory that relates to the crossing number of a graph, which is a measure of how many edges of the graph cross each other when the graph is drawn in the plane. The crossing number, denoted as \( cr(G) \), of a graph \( G \) is defined as the minimum number of crossings that occur in any drawing of the graph in the plane.
A **cycle double cover** of a graph is a particular type of subgraph that consists of a collection of cycles in which each edge of the original graph is included in exactly two of these cycles. More formally, for a given graph \( G \), a cycle double cover is a set of cycles such that every edge in \( G \) is covered exactly twice by the cycles in the set.
The left-right planarity test is a method used in graph drawing and computational geometry to determine whether a given graph can be drawn in a plane without edge crossings, specifically in a way that respects a certain left-right ordering of the vertices. In the context of embedded planar graphs, the left-right planarity test deals with directed graphs (digraphs) and attempts to find a planar embedding of the graph such that: 1. Each vertex is placed on a horizontal line.
A "queue number" generally refers to a numerical value assigned to a person or item in a queue (or line), indicating their position relative to others waiting for service, access, or processing. This concept is commonly used in various settings, including: 1. **Customer Service**: In banks, restaurants, and service centers, customers receive queue numbers to organize the order in which they will be served.
The term "rotation system" can refer to several concepts depending on the context in which it is used. Here are a few possibilities: 1. **Mathematics and Physics**: In mathematics, particularly in geometry and physics, a rotation system can refer to a mathematical construct that describes how objects rotate around a point in space. For example, in the context of rigid body dynamics, it often involves the use of rotation matrices or quaternion representations.
A **string graph** is a type of intersection graph that can be constructed from a collection of continuous curves (strings) in a two-dimensional space. More formally, a string graph is defined as the graph whose vertices correspond to these curves, and there is an edge between two vertices if and only if the corresponding curves intersect at some point in the plane.
The Three Utilities Problem is a classic problem in graph theory and combinatorial optimization. It involves connecting three houses to three utility services (like water, electricity, and gas) without any of the utility lines crossing each other. In more formal terms, the problem can be visualized as a bipartite graph where one set contains the three houses and the other set contains the three utilities.
Turán's brick factory problem is a classic problem in combinatorial optimization, particularly in the field of graph theory. It is named after the Hungarian mathematician Paul Erdős and his colleague László Turán, who studied problems involving extremal graph theory. The problem can be described as follows: Imagine a brick factory that produces bricks of various colors.
The Wilson operation, also known as the Wilson loop, is a concept from quantum field theory, particularly in the context of gauge theories. It is named after Kenneth Wilson, who introduced it in the early 1970s as part of his work on lattice gauge theories and the study of confinement in quantum chromodynamics (QCD). In simple terms, the Wilson loop is a gauge-invariant quantity associated with the path of a loop in spacetime.
An **amenable group** is a type of mathematical structure studied in the field of group theory, specifically in the study of topological groups and functional analysis. The concept of amenability is related to the ability of a group to have a certain type of "invariance" property under averaging processes. A group \( G \) is called **amenable** if it has a left-invariant mean.
Chabauty topology is a concept used in algebraic geometry and arithmetic geometry, specifically in the study of the spaces of subvarieties of algebraic varieties. It is named after the mathematician Claude Chabauty, who developed this topology in the context of algebraic varieties and their rational points. In the Chabauty topology, one can think about the space of closed subsets of a given topological space (often within a certain context such as algebraic varieties).
A **continuous group action** is a mathematical concept that arises in the field of topology and group theory. Specifically, it involves a group acting on a topological space in a way that is compatible with the topological structure of that space. ### Definition: Let \( G \) be a topological group and \( X \) be a topological space.
In group theory, a branch of abstract algebra, a **covering group** is a concept that relates to the idea of covering spaces in topology, though it is used more specifically in the context of group representations and algebraic structures. A covering group can refer to a group that serves as a double cover of another group in the sense of group homomorphisms.
The Grothendieck–Riemann–Roch theorem is a fundamental result in algebraic geometry and algebraic topology that extends classical Riemann–Roch theorems for curves to more general situations, particularly for algebraic varieties. The theorem originates from the work of Alexander Grothendieck in the 1950s and provides a powerful tool for calculating the dimensions of certain cohomology groups.
Bott periodicity theorem is a central result in stable homotopy theory, named after the mathematician Raoul Bott. The theorem essentially states that the homotopy groups of certain topological spaces exhibit periodic behavior. More specifically, Bott periodicity is concerned with the stable homotopy groups of spheres and the stable homotopy classification of certain types of vector bundles.
The National Wind Institute (NWI) is a research and education organization based at Texas Tech University in Lubbock, Texas. It focuses on the study of wind-related phenomena, including wind energy, wind engineering, and the effects of wind on structures. The NWI aims to improve safety and resilience against severe wind events, such as tornadoes and hurricanes, as well as to promote the development of wind energy technologies.
The term "Power Flash" can refer to different things depending on the context: 1. **Technology and Electronics**: In some technical contexts, "Power Flash" might refer to a rapid surge of electrical power, perhaps used in relation to systems that require brief high-power bursts, such as in certain motors or power supplies.