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9 votes
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Are there fast rank and unrank algorithms for integer vectors under the action of a permutation group?

We are distributing $m$ indistinguishable balls in $k$ numbered boxes $S=\{1,2,\ldots,k\}$. A distribution is a tuple of nonnegative integers $a=(a_1,\ldots,a_k)$ whose sum is $m$. We also have a ...
Jukka Kohonen's user avatar
6 votes
0 answers
115 views

Distribution of peaks in permutations, after a sorting operation

Let $S_n$ be the set of permutations on $\{1,2,\dotsc,n\}$. A peak-value of $\pi$ is some $\pi_i$ such that $\pi_{i-1} < \pi_i > \pi_{i+1}$, where $1<i<n$. Let $PV(\pi)$ denote the set of ...
Per Alexandersson's user avatar