出典:Wikipedia
出典:『Wikipedia』 (2010/05/15 03:29 UTC 版)
In graph theory, nowhere-zero flows are a special type of network flow which is related (by duality) to coloring planar graphs. Let G = (V,E) be a directed graph and let M be an abelian group. We say that a map
is a flow or an M-flow if the following condition (sometimes called the Kirchoff Rule) is satisfied at every vertex
(here we let δ + (v) denote the set of edges pointing away from v and δ − (v) the set of edges pointing toward v).