$k$-distant crossings and nestings of matchings and partitions
Abstract
Description
We define and consider k-distant crossings and nestings for matchings and set partitions, which are a variation of crossings and nestings in which the distance between vertices is important. By modifying an involution of Kasraoui and Zeng (Electronic J. Combinatorics 2006, research paper 33), we show that the joint distribution of k-distant crossings and nestings is symmetric. We also study the numbers of k-distant noncrossing matchings and partitions for small k, which are counted by well-known sequences, as well as the orthogonal polynomials related to k-distant noncrossing matchings and partitions. We extend Chen et al.'s r-crossings and enhanced r-crossings.
16 pages, 4 figures, Sage code appendix; v2: fix a couple typos, thanks Philippe Nadeau; v3: fix more typos, accepted for FPSAC 2009
16 pages, 4 figures, Sage code appendix; v2: fix a couple typos, thanks Philippe Nadeau; v3: fix more typos, accepted for FPSAC 2009