Galois connection: Difference between revisions

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en>Jochen Burghardt
→‎Applications in the theory of programming: deleted ref. to own paper, awaiting discussion on talk page
en>VictorPorton
Added a definition of Galois correspondence
 
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In [[geometry]], a '''cuboid''' is a [[convex polyhedron]] bounded by six [[quadrilateral]] faces, whose [[polyhedral graph]] is the same as that of a [[cube]]. While some mathematical literature refers to any such polyhedron as a cuboid,<ref>{{citation|title=Polytopes and Symmetry|first=Stewart Alexander|last=Robertson|publisher=Cambridge University Press|year=1984|isbn=978-0-521-27739-6|page=75}}</ref> other sources use "cuboid" to refer to a shape of this type in which each of the faces is a [[rectangle]] (and so each pair of adjacent faces meets in a [[right angle]]); this more restrictive type of cuboid is also known as a '''rectangular cuboid''', '''right cuboid''', '''rectangular [[box]]''', '''rectangular [[hexahedron]]''', '''right rectangular prism''', or '''rectangular [[parallelepiped]]'''.<ref>{{citation|title=Elements of Synthetic Solid Geometry|first=Nathan Fellowes|last=Dupuis|publisher=Macmillan|year=1893|page=53}}</ref>
 
==General cuboids==
By [[Euler characteristic|Euler's formula]] the number of faces ('F'), vertices (''V''), and edges (''E'') of any convex polyhedron are related by the formula "F + V " = E + 2 . In the case of a cuboid this gives 6 + 8  = 12 + 2; that is, like a cube, a cuboid has 6 [[Face (geometry)|faces]], 8 [[vertex (geometry)|vertices]], and 12 edges.
 
Along with the rectangular cuboids, any [[parallelepiped]] is a cuboid of this type, as is a square [[frustum]] (the shape formed by truncation of the apex of a [[square pyramid]]).
 
==Rectangular cuboid==
 
{| cellpadding="5"  style="background:#fff; float:right; margin-left:10px; width:250px;" class="wikitable"
|-
! style="background:#e7dcc3;" colspan="2"|Rectangular cuboid
|-
|colspan=2|[[File:Cuboid simple.svg|240px|Rectangular cuboid]]
|-
| style="background:#aeae74;"|Type||[[Prism (geometry)|Prism]]
|-
| style="background:#e7dcc3;"|Faces||6 [[rectangle]]s
|-
| style="background:#e7dcc3;"|Edges||12
|-
| style="background:#e7dcc3;"|Vertices||8
|-
| style="background:#e7dcc3;"|[[List of spherical symmetry groups|Symmetry group]]||[[Dihedral symmetry|''D''<sub>''2h''</sub>]], [2,2], (*222), order 8
|-
| style="background:#e7dcc3;"|[[Schläfli symbol]]||{&nbsp;}×{&nbsp;}×{&nbsp;} or {&nbsp;}<sup>3</sup>
|-
| style="background:#e7dcc3;"|[[Coxeter diagram]]||{{CDD|node_1|2|node_1|2|node_1}}
|-
| style="background:#e7dcc3;"|[[Dual polyhedron]]||Rectangular fusil
|-
| style="background:#e7dcc3;"|Properties||[[Convex polyhedron|convex]], [[zonohedron]], [[isogonal figure|isogonal]]
|}In a rectangular cuboid, all angles are [[right angle]]s, and opposite faces of a cuboid are [[congruence (geometry)|equal]]. It is also a '''right rectangular [[Prism (geometry)|prism]]'''. The term "rectangular or oblong prism" is ambiguous. Also the term ''rectangular [[parallelepiped]]'' or orthogonal parallelepiped is used.
 
The '''square cuboid''', '''square box''', or '''right square prism''' (also ambiguously called ''square prism'') is a special case of the cuboid in which at least two faces are squares. The [[cube (geometry)|cube]] is a special case of the square cuboid in which all six faces are squares.
 
If the dimensions of a cuboid are ''a'', ''b'' and ''c'', then its [[volume]] is ''abc'' and its [[surface area]] is 2''ab'' + 2''ac'' + 2''bc''.
 
The length of the [[space diagonal]] is
:<math>d = \sqrt{a^2+b^2+c^2}.\ </math>
 
Cuboid shapes are often used for [[box]]es, [[cupboard]]s, [[Room (architecture)|room]]s, buildings, etc. Cuboids are among those solids that can [[Honeycomb (geometry)|tessellate 3-dimensional space]]. The shape is fairly versatile in being able to contain multiple smaller cuboids, e.g. [[sugar]] cubes in a box, boxes in a cupboard, cupboards in a room, and rooms in a building.
 
A cuboid with integer edges as well as integer face diagonals is called an [[Euler brick]], for example with sides 44, 117 and 240.
A [[Euler brick#Perfect cuboid|perfect cuboid]] is an Euler brick whose space diagonal is also an integer.  It is currently unknown whether a perfect cuboid actually exists.
 
== See also ==
* [[Cube]]
* [[Hyperrectangle]]
* [[Rectangle]]
* [[Trapezohedron]]
 
==References==
{{reflist}}
 
== External links ==
{{Commons category|Cuboids}}
* {{MathWorld | urlname=Cuboid | title=Cuboid}}
* [http://www.korthalsaltes.com/model.php?name_en=rectangular%20prism Rectangular prism and cuboid] Paper models and pictures
{{Polyhedron navigator}}
[[Category:Elementary shapes]]
[[Category:Polyhedra]]
[[Category:Prismatoid polyhedra]]
[[Category:Space-filling polyhedra]]
[[Category:Zonohedra]]

Latest revision as of 22:14, 13 October 2014

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