Restricted Stirling and Lah number matrices and their inverses
Abstract
Given let , , and be the number of ways of partitioning the set into non-empty subsets, cycles and lists, respectively, with each block having cardinality in . We refer to these as the -restricted Stirling numbers of the second and first kind and the -restricted Lah numbers, respectively. Note that the classical Stirling numbers of the second kind and first kind, and Lah numbers are , and , respectively. The matrices , and have inverses , and respectively. The inverse matrices , and exist if and only if . We express each entry of each of these matrices as the difference between the cardinalities of two explicitly defined families of labeled forests. In particular the entries of have combinatorial interpretations, affirmatively answering a question of Choi, Long, Ng and Smith from 2006. If and if for all with odd and , we have , we additionally show that each entry of , and is up to an explicit sign the cardinality of a single explicitly defined family of labeled forests. Our results also provide combinatorial interpretations of the th Whitney numbers of the first and second kinds of , the poset of partitions of that have each part size congruent to mod .
Keywords
Cite
@article{arxiv.1610.05803,
title = {Restricted Stirling and Lah number matrices and their inverses},
author = {John Engbers and David Galvin and Clifford Smyth},
journal= {arXiv preprint arXiv:1610.05803},
year = {2018}
}
Comments
This is a substantial revision of version 1, with more extensive results and unified proofs, as well as with new connections to certain Whitney numbers