English

Nilpotent matrices having a given Jordan type as maximum commuting nilpotent orbit

Rings and Algebras 2018-03-15 v3 Commutative Algebra Representation Theory

Abstract

The Jordan type of a nilpotent matrix is the partition giving the sizes of its Jordan blocks. We study pairs of partitions (P,Q)(P,Q), where Q=Q(P)Q={\mathcal Q}(P) is the Jordan type of a generic nilpotent matrix A commuting with a nilpotent matrix B of Jordan type P P. T. Ko\v{s}ir and P. Oblak have shown that QQ has parts that differ pairwise by at least two. Such partitions, which are also known as "super distinct" or "Rogers-Ramanujan", are exactly those that are stable or "self-large" in the sense that Q(Q)=Q{\mathcal Q}(Q)=Q. In 2012 P. Oblak formulated a conjecture concerning the cardinality of the set of partitions PP such that Q(P){\mathcal Q}(P) is a given stable partition Q Q with two parts, and proved some special cases. R. Zhao refined this to posit that those partitions PP such that Q(P)=Q=(u,ur){\mathcal Q}(P)= Q=(u,u-r) with u>r2u>r\ge 2 could be arranged in an (r1)(r-1) by (ur)(u-r) table T(Q){\mathcal T}(Q) where the entry in the kk-th row and \ell-th column has k+k+\ell parts. We prove this Table Theorem, and then generalize the statement to propose a Box Conjecture for the set of partitions PP for which Q(P)=Q{\mathcal Q}(P)=Q, for an arbitrary stable partition QQ.

Keywords

Cite

@article{arxiv.1409.2192,
  title  = {Nilpotent matrices having a given Jordan type as maximum commuting nilpotent orbit},
  author = {Anthony Iarrobino and Leila Khatami and Bart Van Steirteghem and Rui Zhao},
  journal= {arXiv preprint arXiv:1409.2192},
  year   = {2018}
}

Comments

v1: 48 pages, 8 figures ; v2: 61 pages, 7 figures, colors used in tables, improved exposition, details added to some proofs; v3: 48 pages, shortened for submission, then extensively revised for clarity/corrected after substantial referee comments

R2 v1 2026-06-22T05:50:49.159Z