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Counting restricted orientations of random graphs
Authors:Maurício Collares  Yoshiharu Kohayakawa  Robert Morris  Guilherme O Mota
Abstract:We count orientations of urn:x-wiley:rsa:media:rsa20904:rsa20904-math-0001 avoiding certain classes of oriented graphs. In particular, we study urn:x-wiley:rsa:media:rsa20904:rsa20904-math-0002, the number of orientations of the binomial random graph urn:x-wiley:rsa:media:rsa20904:rsa20904-math-0003 in which every copy of urn:x-wiley:rsa:media:rsa20904:rsa20904-math-0004 is transitive, and urn:x-wiley:rsa:media:rsa20904:rsa20904-math-0005, the number of orientations of urn:x-wiley:rsa:media:rsa20904:rsa20904-math-0006 containing no strongly connected copy of urn:x-wiley:rsa:media:rsa20904:rsa20904-math-0007. We give the correct order of growth of urn:x-wiley:rsa:media:rsa20904:rsa20904-math-0008 and urn:x-wiley:rsa:media:rsa20904:rsa20904-math-0009 up to polylogarithmic factors; for orientations with no cyclic triangle, this significantly improves a result of Allen, Kohayakawa, Mota, and Parente. We also discuss the problem for a single forbidden oriented graph, and state a number of open problems and conjectures.
Keywords:restricted orientations  random graphs  forbidden digraphs
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