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Partial Geometry
An incidence structure C=(P,L,I) consists of points P, lines L, and flags I \subseteq P \times L where a point p is said to be incident with a line l if (p,l) \in I. It is a (finite) partial geometry if there are integers s,t,\alpha\geq 1 such that: * For any pair of distinct points p and q, there is at most one line incident with both of them. * Each line is incident with s+1 points. * Each point is incident with t+1 lines. * If a point p and a line l are not incident, there are exactly \alpha pairs (q,m)\in I, such that p is incident with m and q is incident with l. A partial geometry with these parameters is denoted by pg(s,t,\alpha). Properties * The number of points is given by \frac and the number of lines by \frac. * The point graph (also known as the collinearity graph) of a pg(s,t,\alpha) is a strongly regular graph: srg((s+1)\frac,s(t+1),s-1+t(\alpha-1),\alpha(t+1)). * Partial geometries are dual structures: the dual of a pg(s,t,\alpha) is simply a pg(t,s,\alpha). Speci ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Incidence Structure
In mathematics, an incidence structure is an abstract system consisting of two types of objects and a single relationship between these types of objects. Consider the points and lines of the Euclidean plane as the two types of objects and ignore all the properties of this geometry except for the relation of which points are on which lines for all points and lines. What is left is the incidence structure of the Euclidean plane. Incidence structures are most often considered in the geometrical context where they are abstracted from, and hence generalize, planes (such as affine, projective, and Möbius planes), but the concept is very broad and not limited to geometric settings. Even in a geometric setting, incidence structures are not limited to just points and lines; higher-dimensional objects (planes, solids, -spaces, conics, etc.) can be used. The study of finite structures is sometimes called finite geometry. Formal definition and terminology An incidence structure is a triple ( ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Finite
Finite is the opposite of infinite. It may refer to: * Finite number (other) * Finite set, a set whose cardinality (number of elements) is some natural number * Finite verb, a verb form that has a subject, usually being inflected or marked for person and/or tense or aspect * "Finite", a song by Sara Groves from the album ''Invisible Empires'' See also * * Nonfinite (other) Nonfinite is the opposite of finite * a nonfinite verb A nonfinite verb is a derivative form of a verb unlike finite verbs. Accordingly, nonfinite verb forms are inflected for neither number nor person, and they cannot perform action as the root ... {{disambiguation fr:Fini it:Finito ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Integer
An integer is the number zero (), a positive natural number (, , , etc.) or a negative integer with a minus sign (−1, −2, −3, etc.). The negative numbers are the additive inverses of the corresponding positive numbers. In the language of mathematics, the set of integers is often denoted by the boldface or blackboard bold \mathbb. The set of natural numbers \mathbb is a subset of \mathbb, which in turn is a subset of the set of all rational numbers \mathbb, itself a subset of the real numbers \mathbb. Like the natural numbers, \mathbb is countably infinite. An integer may be regarded as a real number that can be written without a fractional component. For example, 21, 4, 0, and −2048 are integers, while 9.75, , and are not. The integers form the smallest group and the smallest ring containing the natural numbers. In algebraic number theory, the integers are sometimes qualified as rational integers to distinguish them from the more general algebraic integers ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Collinearity
In geometry, collinearity of a set of Point (geometry), points is the property of their lying on a single Line (geometry), line. A set of points with this property is said to be collinear (sometimes spelled as colinear). In greater generality, the term has been used for aligned objects, that is, things being "in a line" or "in a row". Points on a line In any geometry, the set of points on a line are said to be collinear. In Euclidean geometry this relation is intuitively visualized by points lying in a row on a "straight line". However, in most geometries (including Euclidean) a Line (geometry), line is typically a Primitive notion, primitive (undefined) object type, so such visualizations will not necessarily be appropriate. A Mathematical model, model for the geometry offers an interpretation of how the points, lines and other object types relate to one another and a notion such as collinearity must be interpreted within the context of that model. For instance, in spherical ge ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Strongly Regular Graph
In graph theory, a strongly regular graph (SRG) is defined as follows. Let be a regular graph with vertices and degree . is said to be strongly regular if there are also integers and such that: * Every two adjacent vertices have common neighbours. * Every two non-adjacent vertices have common neighbours. The complement of an is also strongly regular. It is a . A strongly regular graph is a distance-regular graph with diameter 2 whenever μ is non-zero. It is a locally linear graph whenever . Etymology A strongly regular graph is denoted an srg(''v'', ''k'', λ, μ) in the literature. By convention, graphs which satisfy the definition trivially are excluded from detailed studies and lists of strongly regular graphs. These include the disjoint union of one or more equal-sized complete graphs, and their complements, the complete multipartite graphs with equal-sized independent sets. Andries Brouwer and Hendrik van Maldeghem (see #References) use an alternate but fu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Generalized Quadrangle
In geometry, a generalized quadrangle is an incidence structure whose main feature is the lack of any triangles (yet containing many quadrangles). A generalized quadrangle is by definition a polar space of rank two. They are the with ''n'' = 4 and near 2n-gons with ''n'' = 2. They are also precisely the partial geometries pg(''s'',''t'',α) with α = 1. Definition A generalized quadrangle is an incidence structure (''P'',''B'',I), with I ⊆ ''P'' × ''B'' an incidence relation, satisfying certain axioms. Elements of ''P'' are by definition the ''points'' of the generalized quadrangle, elements of ''B'' the ''lines''. The axioms are the following: * There is an ''s'' (''s'' ≥ 1) such that on every line there are exactly ''s'' + 1 points. There is at most one point on two distinct lines. * There is a ''t'' (''t'' ≥ 1) such that through every point there are exactly ''t'' + 1 lines. There is at most one line through two distinct points. * For every point ''p'' not on a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Steiner System
250px, thumbnail, The Fano plane is a Steiner triple system S(2,3,7). The blocks are the 7 lines, each containing 3 points. Every pair of points belongs to a unique line. In combinatorial mathematics, a Steiner system (named after Jakob Steiner) is a type of block design, specifically a t-design with λ = 1 and ''t'' = 2 or (recently) ''t'' ≥ 2. A Steiner system with parameters ''t'', ''k'', ''n'', written S(''t'',''k'',''n''), is an ''n''-element set ''S'' together with a set of ''k''-element subsets of ''S'' (called blocks) with the property that each ''t''-element subset of ''S'' is contained in exactly one block. In an alternate notation for block designs, an S(''t'',''k'',''n'') would be a ''t''-(''n'',''k'',1) design. This definition is relatively new. The classical definition of Steiner systems also required that ''k'' = ''t'' + 1. An S(2,3,''n'') was (and still is) called a ''Steiner triple'' (or ''triad'') ''system'', while an S(3,4,''n'') is called a ''Steiner quad ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Partial Linear Space
A partial linear space (also semilinear or near-linear space) is a basic incidence structure in the field of incidence geometry, that carries slightly less structure than a linear space. The notion is equivalent to that of a linear hypergraph. Definition Let S=(,, \textbf) an incidence structure, for which the elements of are called ''points'' and the elements of are called ''lines''. ''S'' is a partial linear space, if the following axioms hold: * any line is incident with at least two points * any pair of distinct points is incident with at most one line If there is a unique line incident with every pair of distinct points, then we get a linear space. Properties The De Bruijn–Erdős theorem shows that in any finite linear space S=(,, \textbf) which is not a single point or a single line, we have , \mathcal, \leq , \mathcal, . Examples * Projective space * Affine space * Polar space * Generalized quadrangle * Generalized polygon * Near polygon References * . *Lynn Bat ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Strongly Regular Graph
In graph theory, a strongly regular graph (SRG) is defined as follows. Let be a regular graph with vertices and degree . is said to be strongly regular if there are also integers and such that: * Every two adjacent vertices have common neighbours. * Every two non-adjacent vertices have common neighbours. The complement of an is also strongly regular. It is a . A strongly regular graph is a distance-regular graph with diameter 2 whenever μ is non-zero. It is a locally linear graph whenever . Etymology A strongly regular graph is denoted an srg(''v'', ''k'', λ, μ) in the literature. By convention, graphs which satisfy the definition trivially are excluded from detailed studies and lists of strongly regular graphs. These include the disjoint union of one or more equal-sized complete graphs, and their complements, the complete multipartite graphs with equal-sized independent sets. Andries Brouwer and Hendrik van Maldeghem (see #References) use an alternate but fu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Maximal Arc
A Maximal arc in a finite projective plane is a largest possible (''k'',''d'')-arc in that projective plane. If the finite projective plane has order ''q'' (there are ''q''+1 points on any line), then for a maximal arc, ''k'', the number of points of the arc, is the maximum possible (= ''qd'' + ''d'' - ''q'') with the property that no ''d''+1 points of the arc lie on the same line. Definition Let \pi be a finite projective plane of order ''q'' (not necessarily desarguesian). Maximal arcs of ''degree'' ''d'' ( 2 ≤ ''d'' ≤ ''q''- 1) are (''k'',''d'')- arcs in \pi, where ''k'' is maximal with respect to the parameter ''d'', in other words, ''k'' = ''qd'' + ''d'' - ''q''. Equivalently, one can define maximal arcs of degree ''d'' in \pi as non-empty sets of points ''K'' such that every line intersects the set either in 0 or ''d'' points. Some authors permit the degree of a maximal arc to be 1, ''q'' or even ''q''+ 1. Letting ''K'' be a maximal (''k'', ''d'')-arc in a projective p ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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