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Results tagged with co.combinatorics
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user 3545
Enumerative combinatorics, graph theory, order theory, posets, matroids, designs and other discrete structures. It also includes algebraic, analytic and probabilistic combinatorics.
4
votes
0
answers
95
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Counting cycles after permuting within rows and columns
Consider a rectangular $p \times q$ array, labelled by the numbers $0, \ldots, pq - 1$ for convenience. Let $S_p$ and $S_q$ and $S_{pq}$ denote the symmetric groups. Take a family of permutations:
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- 13.3k
19
votes
1
answer
947
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Recognize this strange expression from linear algebra?
I've come across an odd-looking expression and oh how I wish I had a more elegant description of it. Maybe someone who enjoys symmetric bilinear forms in characteristic two will recognize it? Or som …
- 13.3k
13
votes
Count of full, binary trees with fixed number of leaves
This is a very well-known enumeration problem. The number of full binary rooted trees with $n+1$ leaves is just the $n$-th Catalan number $$C_n = \frac{(2n)!}{(n+1)!n!}.$$
You can read more by loo …
- 13.3k