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Enumerative combinatorics, graph theory, order theory, posets, matroids, designs and other discrete structures. It also includes algebraic, analytic and probabilistic combinatorics.

2 votes

Table of planar connected graphs

In Sage, see www.sagemath.org, you find the algorithm G. Brinkmann and B.D. McKay, Fast generation of planar graphs, MATCH-Communications in Mathematical and in Computer Chemistry, 58(2):323-357, 200 …
Christian Stump's user avatar
3 votes

A function from partitions to natural numbers - is it familiar?

Okay, I agree that this answer comes actually a little late... If you type some values of your function into FindStat, you will see David Speyer's answer automatically generated, since it is obtained …
Christian Stump's user avatar
8 votes
Accepted

Parking functions to non-crossing partitions

I still hope there is a complete (and easy) answer to the question, but as mentioned in my comment above, and since no one else answered so far, I give a description of the inverse map that is not com …
Christian Stump's user avatar
6 votes
1 answer
295 views

A bijective proof that the bistatistic $(\operatorname{exc},\operatorname{den})$ on permutat...

In a joint project, we are currently working on an online combinatorial statistic finder in which (beside other things) want to gather information about combinatorial collections and statistic, see th …
Christian Stump's user avatar
6 votes
Accepted

Weighted Permutation Sum

You can search this statistic (normalized so that the smallest value is 0) in www.FindStat.org and you will find that this is the rank of the permutation inside the lattice of alternating sign matrice …
Christian Stump's user avatar
2 votes

Even parking functions and spanning trees of complete bipartite graphs

This is far from an answer, but only a possible first part of such a bijection. (There were two plainly wrong bijection parts in the first version that cannot be fixed.) The bijection between factori …
Christian Stump's user avatar
2 votes

Specialization (of parameters) of Macdonald polynomials and characters of classical groups

You find Macdonald polynomials defined for root systems for example in Macdonald's lecture series "Symmetric functions and orthogonal polynomaials", or as well in various places, like http://en.wikipe …
Christian Stump's user avatar
8 votes

Bijection directly from (n,n+1)-core partitions to parking functions?

Increasing parking functions are in (more or less canonical) bijection with Dyck paths (see, e.g., here), so your question can be rephrased as Is there a direct bijection between (n,n+1)-cores and Dy …
Christian Stump's user avatar
2 votes

the space of noncrossing partitions of S^1

Am I right that you consider $x \mapsto mx$ modulo $mn$? This property is then equivalent to simply consider noncrossing partitions of $\{1,\ldots,mn\}$ where each block has size $n$. Given any multi …
Christian Stump's user avatar
4 votes

Length of the longest chain in dominance order

This is Exercise 7.2(f) in Stanley "Enumerative Combinatorics II": The length of the longest chain in dominance order is $$\frac{1}{3}m(m^2+3r-1)$$ where $n = \binom{m+1}{2} + r$ with $0 \leq r \leq m …
Christian Stump's user avatar
1 vote

Optimal bounds for an alternating sum on a downset

This is more a comment, but here I have more space: Did you try to use the characterization of f-vectors of simplicial complexes given by Kruskal in "Joseph B. Kruskal. The number of simplices in a c …
Christian Stump's user avatar
4 votes

Characterizing posets by functions into natural numbers

If you have given all linear extensions of $\mathcal{L}(P)$ of a poset $P$. This is the set of all linear orderings (permutations) of the vertex set of $P$ preserving the order in $P$. The order in $P …
Christian Stump's user avatar
15 votes
Accepted

A family of words counted by the Catalan numbers

Below my modified answer containing a complete bijection between the above sequences and Dyck paths: Let $a = (a_1,\ldots,a_n)$ be a sequence of $n$ integers. $a$ satisfies Property $A$ if it satisfi …
Christian Stump's user avatar
2 votes
0 answers
85 views

An EKR type card deck of a childrens card game

You want to print a deck of cards of the following type: Each card shows $k$ items out of $n$ different items such that any two cards in the deck share exactly one item. Question: What is the bigg …
Christian Stump's user avatar
2 votes
Accepted

Indexing combinations with repetition

@PietroMajer's comment essentially contained the answer already: Define a bijection $\phi$ between $k$-multisubsets of $\{ 1,\ldots,n \}$ to $k$-subsets of $\{ 1,\ldots,n+k-1\}$ by sending $\{ c_0 \l …
Christian Stump's user avatar

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