48 research outputs found
Elliptic rook and file numbers
Utilizing elliptic weights, we construct an elliptic analogue of rook numbers
for Ferrers boards. Our elliptic rook numbers generalize Garsia and Remmel's
q-rook numbers by two additional independent parameters a and b, and a nome p.
These are shown to satisfy an elliptic extension of a factorization theorem
which in the classical case was established by Goldman, Joichi and White and
later was extended to the q-case by Garsia and Remmel. We obtain similar
results for our elliptic analogues of Garsia and Remmel's q-file numbers for
skyline boards. We also provide an elliptic extension of the j-attacking model
introduced by Remmel and Wachs. Various applications of our results include
elliptic analogues of (generalized) Stirling numbers of the first and second
kind, Lah numbers, Abel numbers, and r-restricted versions thereof.Comment: 45 pages; 3rd version shortened (elliptic rook theory for matchings
has been taken out to keep the length of this paper reasonable
Classification of Ding's Schubert Varieties: Finer Rook Equivalence
First published in The Canadian Journal of Mathematics, volume 59, no. 1, 2007, published by the Canadian Mathematical Society.K.~Ding studied a class of Schubert varieties in type A partial flag manifolds, indexed by integer partitions \lambda and in bijection with dominant permutations. He observed that the Schubert cell structure of X_\lambda is indexed by maximal rook placements on the Ferrers board B_\lambda, and that the integral cohomology groups H^*(X_\lambda;\:\Zz), H^*(X_\mu;\:\Zz) are additively isomorphic exactly when the Ferrers boards B_\lambda, B_\mu satisfy the combinatorial condition of \emph{rook-equivalence}. We classify the varieties X_\lambda up to isomorphism, distinguishing them by their graded cohomology rings with integer coefficients. The crux of our approach is studying the nilpotence orders of linear forms in the cohomology ring
Bruhat intervals as rooks on skew Ferrers boards
We characterise the permutations pi such that the elements in the closed
lower Bruhat interval [id,pi] of the symmetric group correspond to non-taking
rook configurations on a skew Ferrers board. It turns out that these are
exactly the permutations pi such that [id,pi] corresponds to a flag manifold
defined by inclusions, studied by Gasharov and Reiner.
Our characterisation connects the Poincare polynomials (rank-generating
function) of Bruhat intervals with q-rook polynomials, and we are able to
compute the Poincare polynomial of some particularly interesting intervals in
the finite Weyl groups A_n and B_n. The expressions involve q-Stirling numbers
of the second kind.
As a by-product of our method, we present a new Stirling number identity
connected to both Bruhat intervals and the poly-Bernoulli numbers defined by
Kaneko.Comment: 16 pages, 9 figure
-Rook polynomials and matrices over finite fields
Connections between -rook polynomials and matrices over finite fields are
exploited to derive a new statistic for Garsia and Remmel's -hit polynomial.
Both this new statistic and another statistic for the -hit polynomial
recently introduced by Dworkin are shown to induce different multiset
Mahonian permutation statistics for any Ferrers board. In addition, for the
triangular boards they are shown to generate different families of
Euler-Mahonian statistics. For these boards the family includes Denert's
statistic , and gives a new proof of Foata and Zeilberger's Theorem that
is jointly distributed with . The family appears
to be new. A proof is also given that the -hit polynomials are symmetric and
unimodal