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・ POlarization Emission of Millimeter Activity at the Sun
・ Polarization identity
・ Polarization in astronomy
・ Polarization mixing
・ Polarization mode dispersion
・ Polarization of an algebraic form
・ Polarization ripples
・ Polarization rotator
・ Polarization scrambling
・ Polarization spectroscopy
・ Polarization-division multiplexing
・ Polarization-maintaining optical fiber
・ Polarized 3D system
・ Polarized light microscopy
・ Polar sine
Polar space
・ Polar Star (Decembrist journal)
・ Polar Star (novel)
・ Polar Star (song)
・ Polar Star Expeditions
・ Polar stratospheric cloud
・ Polar Studios
・ Polar Subglacial Basin
・ Polar Sun Spire
・ Polar surface area
・ Polar T3 syndrome
・ Polar Tankers, Inc. v. City of Valdez
・ Polar the Titanic Bear
・ Polar Times Glacier
・ Polar topology


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Polar space : ウィキペディア英語版
Polar space
In mathematics, in the field of geometry, a polar space of rank ''n'' (), or ''projective index'' , consists of a set ''P'', conventionally the set of points, together with certain subsets of ''P'', called ''subspaces'', that satisfy these axioms:
* Every subspace is isomorphic to a projective geometry with and ''K'' a division ring. By definition, for each subspace the corresponding ''d'' is its dimension.
* The intersection of two subspaces is always a subspace.
* For each point ''p'' not in a subspace ''A'' of dimension of , there is a unique subspace ''B'' of dimension such that is -dimensional. The points in are exactly the points of ''A'' that are in a common subspace of dimension 1 with ''p''.
* There are at least two disjoint subspaces of dimension .
It is possible to define and study a slightly bigger class of objects using only relationship between points and lines: a polar space is a partial linear space (''P'',''L''), so that for each point ''p'' ∈ ''P'' and
each line ''l'' ∈ ''L'', the set of points of ''l'' collinear to ''p'', is either a singleton or the whole ''l''.
A polar space of rank two is a generalized quadrangle; in this case in the latter definition the set of points of a line ''l'' collinear to a point ''p'' is the whole ''l'' only if ''p ∈ l''. One recovers the former definition from the latter under assumptions that lines have more than 2 points, points lie on more than 2 lines, and there exist a line ''l'' and a point ''p'' not on ''l'' so that ''p'' is collinear to all points of ''l''.
Finite polar spaces (where ''P'' is a finite set) are also studied as combinatorial objects.
== Examples==

* In a finite projective space over the field of size ''q'', with ''d'' odd and , the set of all points, with as subspaces the totally isotropic subspaces of an arbitrary symplectic polarity, forms a polar space of rank .
* Let ''Q'' be a nonsingular quadric in with character ω. Then the index of ''Q'' will be . The set of all points on the quadric, together with the subspaces on the quadric, forms a polar space of rank .
* Let ''H'' be a nonsingular Hermitian variety in . The index of ''H'' will be \left\lfloor \frac\right\rfloor. The points on ''H'', together with the subspaces on it, form a polar space of rank \left\lfloor\frac\right\rfloor.

抄文引用元・出典: フリー百科事典『 ウィキペディア(Wikipedia)
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