Dominance Order - Properties of The Dominance Ordering

Properties of The Dominance Ordering

  • Among the partitions of n, (1,…,1) is the smallest and (n) is the largest.
  • The dominance ordering implies lexicographical ordering, i.e. if p dominates q and pq, then for the smallest i such that piqi one has pi > qi.
  • The poset of partitions of n is linearly ordered (and is equivalent to lexicographical ordering) if and only if n ≤ 5. It is graded if and only if n ≤ 6. See image at right for an example.
  • A partition p covers a partition q if and only if pi = qi + 1, pk = qk − 1, pj = qj for all ji,k and either (1) k = i + 1 or (2) qi = qk (Brylawski, Prop. 2.3). Starting from the Young diagram of q, the Young diagram of p is obtained from it by first removing the last box of row k and then appending it either to the end of the immediately preceding row k − 1, or to the end of row i < k if the rows i through k of the Young diagram of q all have the same length.
  • Every partition p has a conjugate (or dual) partition p′, whose Young diagram is the transpose of the Young diagram of p. This operation reverses the dominance ordering:
if and only if
  • The dominance ordering determines the inclusions between the Zariski closures of the conjugacy classes of nilpotent matrices.

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