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Given a positive integer n and a real number p ∈ [0,1], let D(n,p) denote the random digraph defined in the following way: each of the binom(n,2) possible edges on the vertex set {1,2,3,…,n} is included with probability 2p, where all edges are independent of each other. Thereafter, a direction is chosen independently for each edge, with probability 1/2 for each possible direction. In this paper, we study the probability that a random instance of D(n,p) is acyclic, i.e., that it does not contain a directed cycle. We find precise asymptotic formulas for the probability of a random digraph being acyclic in the sparse regime, i.e., when np = O(1). As an example, for each real number μ, we find an exact analytic expression for φ(μ) = lim_{n→ ∞} n^{1/3} ℙ{D(n,1/n (1+μ n^{-1/3})) is acyclic}.
@InProceedings{ralaivaosaona_et_al:LIPIcs.AofA.2020.25,
author = {Ralaivaosaona, Dimbinaina and Rasendrahasina, Vonjy and Wagner, Stephan},
title = {{On the Probability That a Random Digraph Is Acyclic}},
booktitle = {31st International Conference on Probabilistic, Combinatorial and Asymptotic Methods for the Analysis of Algorithms (AofA 2020)},
pages = {25:1--25:18},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-147-4},
ISSN = {1868-8969},
year = {2020},
volume = {159},
editor = {Drmota, Michael and Heuberger, Clemens},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.AofA.2020.25},
URN = {urn:nbn:de:0030-drops-120557},
doi = {10.4230/LIPIcs.AofA.2020.25},
annote = {Keywords: Random digraphs, acyclic digraphs, asymptotics}
}