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From an answer to this question I have learned how to ask this question properly.

Consider a $k$-uniform hypergraph on $n$ nodes, i.e. a family of $k$-subsets of $[n]= \{1,2,\dots,n\}$ (the hyperedges).

Consider a sequence $\langle a_1, a_2, \dots a_n \rangle$ giving the numbers of hyperedges that node $i\in [n]$ is contained in. In the case of $k=2$ this is the classical degree sequence. So let me call the sequence a hyper-degree sequence when $k\leq n$ is arbitrary.

It obviously holds that $a_i \leq \binom{n-1}{k-1}$.

For $k=2$ we know by the handshaking lemma that $\sum_i a_i = 0 \text{ mod } 2$, and I assume that this holds for all $k$: $\sum_i a_i = 0 \text{ mod } k$.

My question is fourfold:

  • What's the best known algorithm (probably not "efficient") to check if a given sequence $\langle a_1, a_2, \dots a_n \rangle$ with $a_i \leq \binom{n-1}{k-1}$ and $\sum_i a_i = 0 \text{ mod } k$ is the hyper-degree sequence of some $k$-uniform hypergraph on $n$ nodes?

  • Even though it may be hard to tell exactly how many of such sequences are hyper-degree sequences, there may be a definite fraction for $n \rightarrow \infty$. How could this fraction be calculated?

  • Before delving into this: Are there further simple necessary conditions for a sequence to be a hyper-degree sequence? For example, for $k=2$ there must be at least $\alpha$ nodes $i \neq 1$ with $a_i \geq 1$ when $a_1 = \alpha$.

  • Finally: How do I construct a $k$-uniform hypergraph for a given hyper-degree sequence?

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  • $\begingroup$ For counting them do you want your degree sequences sorted nonincreasing? It seems now the degree sequence of $\{12, 23\}$ would be $(1,2,1)$ as defined in the question. $\endgroup$ Commented Aug 14, 2020 at 1:58
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    $\begingroup$ @JohnMachacek: You are right, I should have been explicit about sorting, and yes, I want my degree sequences sorted. $\endgroup$ Commented Aug 14, 2020 at 13:48

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Alexander Dewdney generalized the Havel--Hakimi algorithm for standard graph degree sequences to hypergraphs in 1975: Degree seqences in complexes and hypergraphs, Proc. Amer. Math. Soc. 53, 535-540.

You might also look at Sarah Behrens et al., New results of degree sequences of uniform hypergraphs, Electron. J. Combin. 20 (2013) P14.

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  • $\begingroup$ How do you propose turning Dewdney's result into an algorithm without a brute-force search for $(k-1)$-graphic sequences that satisfy the theorem? $\endgroup$ Commented Aug 13, 2020 at 16:57
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    $\begingroup$ This paper seems relevant https://arxiv.org/abs/1706.03951 $\endgroup$
    – Louis D
    Commented Aug 14, 2020 at 1:04

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