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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 …
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 …
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 …
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 …
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 …
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 …
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 …
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 …
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 …
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 …
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 …
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 …
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 …
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 …
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 …