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Difference between revisions of "Packing"

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{{MSC|52C20,52C22}}
 
{{MSC|52C20,52C22}}
{{TEX|part}}  \( \def \Z { {\cal Z}} \)
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{{TEX|done}}  \( \def \Z { {\cal Z}} \)
  
 
A '''packing''' of a (finite or infinite) family of sets $M_i$ in a set $A$ is, in its strict sense,
 
A '''packing''' of a (finite or infinite) family of sets $M_i$ in a set $A$ is, in its strict sense,
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and then this condition is relaxed to requiring only that the interiors of the sets are pairwise disjoint.
 
and then this condition is relaxed to requiring only that the interiors of the sets are pairwise disjoint.
  
=== Lattice packings ===
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==== Lattice packings ====
  
 
As a special case, in vector spaces $V$, such as $\R^d$,
 
As a special case, in vector spaces $V$, such as $\R^d$,
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In particular, such packings are investigated in the geometry of numbers and in discrete geometry.
 
In particular, such packings are investigated in the geometry of numbers and in discrete geometry.
  
=== Sphere packings ===
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==== Sphere packings ====
  
 
Packings of congruent spheres are considered both in the geometry of numbers
 
Packings of congruent spheres are considered both in the geometry of numbers
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However, Hales and his team are working on a computer-verifyable version of the proof.
 
However, Hales and his team are working on a computer-verifyable version of the proof.
  
=== Tilings ===
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==== Tilings ====
  
 
A '''[[tiling]]''' is a packing without gaps,
 
A '''[[tiling]]''' is a packing without gaps,
 
i.e., such that the $M_i$ are also a covering of $A$.
 
i.e., such that the $M_i$ are also a covering of $A$.
 
----
 
----
 
''(text below not yet revised)''
 
 
 
 
====Comments====
 
Sphere packing has various applications in error-correcting codes (cf. [[Error-correcting code|Error-correcting code]]), the channel coding problem, Steiner systems (cf. [[Steiner system|Steiner system]]), <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/p/p071/p071050/p07105021.png" />-designs, and in the theory of finite groups. The most important special case is the sphere packing in <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/p/p071/p071050/p07105022.png" /> via the [[Leech lattice|Leech lattice]]. Finite and infinite sphere packing in <img align="absmiddle" border="0" src="https://www.encyclopediaofmath.org/legacyimages/p/p071/p071050/p07105023.png" /> has applications in classical and modern crystallography (cf. [[Crystallography, mathematical|Crystallography, mathematical]]).
 
  
 
====References====
 
====References====

Revision as of 01:34, 11 February 2012

2020 Mathematics Subject Classification: Primary: 52C20,52C22 [MSN][ZBL] \( \def \Z { {\cal Z}} \)

A packing of a (finite or infinite) family of sets $M_i$ in a set $A$ is, in its strict sense, any pairwise disjoint family of subsets $M_i\subset A$.

However, in geometry, for packings in Euclidean spaces, on an $n$-dimensional sphere, in a closed domanin, or in some other manifold, the sets $M_i$ are often closed domains, and then this condition is relaxed to requiring only that the interiors of the sets are pairwise disjoint.

Lattice packings

As a special case, in vector spaces $V$, such as $\R^d$, packings of translates $ \{ M+v \mid v \in \Z \} $, of a set $ M \subset V $ (also called the packing $(M,\Z)$ of $M$ by $\Z$) are considered. If the set $ \Z \subset V $ of translation vectors is a point lattice, then the packing is called a lattice packing. In particular, such packings are investigated in the geometry of numbers and in discrete geometry.

Sphere packings

Packings of congruent spheres are considered both in the geometry of numbers and in discrete geometry, and have applications in coding theory. A central problem is finding the densest packing, and the densest lattice packing, of congruent spheres in $\R^d$. For $d=3$, the problem (known as Kepler conjecture or Kepler problem) to decide whether there is a better packing than the densest lattice packing was a famous open problem that was recently solved by Hales (1998). With the help of massive computer calculations he showed that the densest lattice packing of spheres is optimal. This result is generally considered as correct but because of its size it has not yet been verified independently. However, Hales and his team are working on a computer-verifyable version of the proof.

Tilings

A tiling is a packing without gaps, i.e., such that the $M_i$ are also a covering of $A$.

References

[1]

E.P. Baranovskii, "Packings, coverings, partitions, and certain other distributions in spaces of constant curvature" Progress in Math. , 9 (1971) pp. 209–253 Itogi Nauk. Algebra. Topol. Geom. 1967 (1969) pp. 181–225

[2]

L. Fejes Toth, "Lagerungen in der Ebene, auf der Kugel und im Raum" , Springer (1972)

[3]

C.A. Rogers, "Packing and covering" , Cambridge Univ. Press (1964)

[4]

J.H. Conway, N.J.A. Sloane, "Sphere packing, lattices and groups" , Springer (1988)

How to Cite This Entry:
Packing. Encyclopedia of Mathematics. URL: http://encyclopediaofmath.org/index.php?title=Packing&oldid=20964
This article was adapted from an original article by A.V. Malyshev (originator), which appeared in Encyclopedia of Mathematics - ISBN 1402006098. See original article