出典:Wiktionary
出典:Wikipedia
出典:『Wikipedia』 (2010/11/18 19:36 UTC 版)
In graph theory, a polytree is a directed graph with at most one undirected path between any two vertices. In other words, a polytree is a directed acyclic graph (DAG) for which there are no undirected cycles either. Equivalently, a polytree is a directed graph formed by giving a direction to each edge of a forest.