Using Rota's Umbral Calculus to Enumerate Stanley's PPartitions
By Shalosh B. Ekhad and Doron Zeilberger
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[Appeared in Advances in Applied Mathematics v. 41 (2008), 206217.]
Dedicated to Two Combinatorial Giants:
GianCarlo Rota ז צ " ל
(April 27, 1932Apri 18, 1999)
and
Richard Stanley ש ל י" ט א
(b. June 23, 1944)
Written: June 12, 2007.
I didn't contribute anything for GianCarlo Rota's 64th birthday collection
or Richard Stanley's 60th birthday
collection, since at the time I didn't have anything relevant,
and I don't like to submit
a paper that is not closely related to the research interests of the honorees.
So this paper is my belated present to these two heroes of mine, and my
coauthor, Shalosh B. Ekhad, really enjoyed computing these lovely brainchildren
of Richard Stanley
using GianCarlo Rota's powerful method of the Umbral Calculus.
Important: This article is accompanied by Maple
package
RotaStanley that computes generating functions enumerating
Ppartitions (in the sense of Stanley) directly, and more impressively,
indirectly, using Rota's Umbral Calculus as it is described in this
article.
Even more impressively, it finds computergenerated functional
recurrences for generating functions of Ppartitions for
families of posets that are obtained by repeated "grafting".
Sample Input and Output For Generating Functions
of Ppartitions for Specific Posets

In order to compute the generating functions (in q) for the
Boolean Lattices of dimensions n=1,2,3, the
input would yield the
output

In order to compute the generating function for Ppartitions for
the lattice of partitions into distinct parts with largest part less than equal to n,
for n=1, 2,3,4, the
input would yield the
output

In order to compute the generating function for Ppartitions for
the Gaussian Lattice G(a,b) (the lattice of partitions into at most
b parts, with each part at most a)
for a,b between 2 and 3, the
input would yield the
output

In order to compute the generating functions, and first few terms, for
solid partitions who live in a 2 by 2 by n by infinity box with n between 2 and 5,
the
input would yield the
output

In order to compute the generating functions, and first few terms, for
staircase shapes (going in either direction), the
input would yield the
output
Sample Input and Output For FunctionalRecurrences
for Generating Functions
of Ppartitions for Powers of a Given Poset
Below are a few examples of computergenerated
functionalrecurrence equations for powers of given posets.
Note that these are fully general theorems. We use
procedure UmbralRecurrenceSingle of the package RotaStanley.

In order to get the functionalrecurrence equation for
powers of the twodimensional Booleanlattice (alias diamond)
where the last vertex of the previous
link is identified with the first one of the next,
the
input would yield the
output

In order to get the functionalrecurrence equation for
powers of the twodimensional Booleanlattice (alias diamond)
where the last two vertices of the previous
link are identified with the first two of the next,
the
input would yield the
output

In order to get the functionalrecurrence equation for
powers of the poset that is a 2rowed tableau each
row with 3 cells, and the bottom row is shifted one
cell to the left,
where the last three vertices of the previous
link are identified with the first three of the next,
the
input would yield the
output

In order to get the functionalrecurrence equation for
powers of the poset that is a 2rowed tableau each
row with 3 cells, and no shift,
where the last three vertices of the previous
link are identified with the first three of the next,
the
input would yield the
output

In order to get the functionalrecurrence equation for
powers of the poset that is a 2rowed tableau each
row with 3 cells, and the bottom row is shifted one
cell to the right,
where the last three vertices of the previous
link are identified with the first three of the next,
the
input would yield the
output

In order to get the functionalrecurrence equation for
powers of a certain hexagon
where the last vertex of the previous
link is identified with the first vertex of the next,
the
input would yield the
output

In order to get the functionalrecurrence equation for
powers of a certain hexagon
where the last two vertices of the previous
link are identified with the first two vertices of the next,
the
input would yield the
output

In order to get the functionalrecurrence equation for
powers of another hexagon where the last vertex of the previous
link is identified with the first vertex of the next, the
input would yield the
output

In order to get the functionalrecurrence equation for
powers of that other hexagon
where the last two vertices of the previous
link are identified with the first two vertices of the next,
the
input would yield the
output
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