Math 2.0

Combinatorics Definition

Neighbourhood

Builds on Graph

Definition

Let GG be a graph with vertex set VV, and let v∈Vv \in V. The neighbourhood of vv is the set N(v)={u∈V:u∼v}N(v) = \{ u \in V : u \sim v \} of the vertices adjacent to vv. The elements of N(v)N(v) are the neighbours of vv.

Remarks

This is the open neighbourhood. It does not contain vv, because no vertex is adjacent to itself. The closed neighbourhood is N[v]=N(v)∪{v}N[v] = N(v) \cup \{v\}. The degree of vv is ∣N(v)∣|N(v)| when N(v)N(v) is finite. In the cycle with vertices 1,2,3,4,51, 2, 3, 4, 5 in this order, N(1)={2,5}N(1) = \{2, 5\}.

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  1. Graph definition
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Where this leads

20 pages build on this one.

Further reading

  1. Web https://en.wikipedia.org/wiki/Neighbourhood_(graph_theory), lead section
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