# Young tableau

*of order *

A Young diagram of order in whose cells the different numbers have been inserted in some order, e.g.

A Young tableau is called standard if in each row and in each column the numbers occur in increasing order. The number of all Young tableau for a given Young diagram of order is equal to and the number of standard Young tableaux is

where the product extends over all the cells of and denotes the length of the corresponding hook.

#### Comments

In Western literature the phrase Ferrers diagram is also used for a Young diagram. In the Russian literature the phrase "Young tableau" ( "Yunga tablitsa" ) and "Young diagram" ( "Yunga diagramma" ) are used precisely in the opposite way, with "tablitsa" referring to the pictorial representation of a partition and "diagramma" being a filled-in "tablitsa" .

Let denote a partition of (, , ) as well as its corresponding Young diagram, its pictorial representation. Let be a second partition of . A -tableau of type is a Young diagram with its boxes filled with 's, 's, etc. For a semi-standard -tableau of type the labelling of the boxes is such that the rows are non-decreasing (from left to right) and the columns are strictly increasing (from top to bottom). E.g.

is a semi-standard -tableau of type . The numbers of semi-standard -tableaux of type are called Kostka numbers.

To each partition of there are associated two "natural" representations of , the symmetric group on letters: the induced representation and the Specht module . The representation is:

where is the trivial representation of and is the Young subgroup of determined by , , where if and otherwise is the subgroup of permutations on the letters .

The group acts on the set of all -tableaux by permuting the labels. Two -tableaux are equivalent if they differ by a permutation of their labels keeping the sets of indices in each row set-wise invariant. An equivalence class of -tableaux is a -tabloid. The action of on -tableaux induces an action on -tabloids, and extending this linearly over a base field gives a representation of which is evidently isomorphic to . The dimension of is . Given a -tableau , let be the following element of :

where is the column-stabilizer of , i.e. the subgroup of of all permutations that leave the labels of the columns of set-wise invariant.

The Specht module, , of is the submodule of spanned by all the elements , where is the tabloid of and is a -tableau. Over a field of characteristic zero the Specht modules give precisely all the different absolutely-irreducible representations of . By Young's rule, the number of times that the Specht module over occurs (as a composition factor) in is equal to the Kostka number . If is the Young symmetrizer of a -tableau , then the Specht module defined by the underlying diagram is isomorphic to the ideal of . This is also (up to isomorphism) the representation denoted by in Representation of the symmetric groups. Cf. Majorization ordering for a number of other results involving partitions, Young diagrams and tableaux, and representations of the symmetric groups.

#### References

[a1] | D. Knuth, "The art of computer programming" , 3 , Addison-Wesley (1973) |

**How to Cite This Entry:**

Young tableau.

*Encyclopedia of Mathematics.*URL: http://encyclopediaofmath.org/index.php?title=Young_tableau&oldid=11610