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Graphs 2.8 - DAGs and Topological Ordering A directed...

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Last Updated: 4/1/10 10:16 AM CSE 2011 Prof. J. Elder - 91 - DAGs and Topological Ordering ± A directed acyclic graph (DAG) is a digraph that has no directed cycles ± A topological ordering of a digraph is a numbering v 1 , …, v n of the vertices such that for every edge ( v i , v j ) , we have i < j ± Example: in a task scheduling digraph, a topological ordering is a task sequence that satisfies the precedence constraints Theorem A digraph admits a topological ordering if and only if it is a DAG B A D C E DAG G B A D C E Topological ordering of G v 1 v 2 v 3 v 4 v 5
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