Extensional acyclic digraphs are acyclic digraphs whose vertices have pairwise different sets of out-neighbors; they represent hereditarily finite sets, which stand at the basis of some computer languages. In this paper we give an O(n^3) algorithm for generating uniformly at random an extensional acyclic digraph on n vertices. This is done by first proposing a linear-time algorithm for encoding such digraphs by particular (n−1)-tuples of subsets of {0,…,n−2}. We then give a new counting recurrence for such tuples, which we exploit in ranking/unranking algorithms. These are also useful for indexing data structures by hereditarily finite sets.

Ranking, unranking and random generation of extensional acyclic digraphs

RIZZI, ROMEO;
2013

Abstract

Extensional acyclic digraphs are acyclic digraphs whose vertices have pairwise different sets of out-neighbors; they represent hereditarily finite sets, which stand at the basis of some computer languages. In this paper we give an O(n^3) algorithm for generating uniformly at random an extensional acyclic digraph on n vertices. This is done by first proposing a linear-time algorithm for encoding such digraphs by particular (n−1)-tuples of subsets of {0,…,n−2}. We then give a new counting recurrence for such tuples, which we exploit in ranking/unranking algorithms. These are also useful for indexing data structures by hereditarily finite sets.
Directed acyclic graph; Extensional digraph; Hereditarily finite sets; Random generation; Graph algorithms; Combinatorial problems
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11562/606353
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