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Plane partition : ウィキペディア英語版
Plane partition

In mathematics and especially in combinatorics, a plane partition is a two-dimensional array of nonnegative integers n_ (with positive integer indices ''i'' and ''j'') that is nonincreasing in both indices, that is, that satisfies
: n_ \ge n_ \quad\mbox\quad n_ \ge n_ \, for all ''i'' and ''j'',
and for which only finitely many of the ''n''''i'',''j'' are nonzero. A plane partitions may be represented visually by the placement of a stack of n_ unit cubes above the point (''i'',''j'') in the plane, giving a three-dimensional solid like the one shown at right.
The ''sum'' of a plane partition is
: n=\sum_ n_ \,
and PL(''n'') denotes the number of plane partitions with sum ''n''.
For example, there are six plane partitions with sum 3:
: \begin 1 & 1 & 1 \end
\qquad \begin 1 & 1 \\ 1 & \end
\qquad \begin 1 \\ 1 \\ 1 & \end
\qquad \begin 2 & 1 & \end
\qquad \begin 2 \\ 1 & \end
\qquad \begin 3 \end

so PL(3) = 6. (Here the plane partitions are drawn using matrix indexing for the coordinates and the entries equal to 0 are suppressed for readability.)
== Ferrers diagrams for plane partitions ==

Another representation for plane partitions is in the form of Ferrers diagrams. The Ferrers diagram of a plane partition of n is a collection of n points or ''nodes'', \lambda=(\mathbf_1,\mathbf_2,\ldots,\mathbf_n), with \mathbf_i\in \mathbb_^ satisfying the condition:〔A. O. L. Atkin, P. Bratley, I. G. Macdonald and J. K. S. McKay, Some computations for ''m''-dimensional partitions, Proc. Camb. Phil. Soc., 63 (1967), 1097–1100.〕
:Condition FD: If the node \mathbf=(a_1,a_2,a_3)\in \lambda, then so do all the nodes \mathbf=(y_1,y_2,y_3) with 0\leq y_i\leq a_i for all i=1,2,3.
Replacing every node of a plane partition by a unit cube with edges aligned with the axes leads to the ''stack of cubes'' representation for the plane partition.

抄文引用元・出典: フリー百科事典『 ウィキペディア(Wikipedia)
ウィキペディアで「Plane partition」の詳細全文を読む



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