Okay, so I think if 2 vertices are adjacent to each other, they are incident to each other....or do I have it wrong? Is this just different terminology. I thought I was totally clear on this for my class, but now I am doubting myself reading the book and looking at my notes. I just want to know if I have it correct, and if I don't could someone explain to me what the difference is between the two. I found several wiki's and different university definitions, but none ever said that the two are alike and I'm confused and would like some reassurance. Thanks in advance.
4 Answers
Usually one speaks of adjacent vertices, but of incident edges.
Two vertices are called adjacent if they are connected by an edge.
Two edges are called incident, if they share a vertex.
Also, a vertex and an edge are called incident, if the vertex is one of the two vertices the edge connects.
If for two vertices $A$ and $B$ there is an edge $e$ joining them, we say that $A$ and $B$ are adjacent.
If two edges $e$ and $f$ have a common vertex $A$, the edges are called incident.
If the vertex $A$ is on edge $e$, the vertex $A$ is often said to be incident on $e$.
There is unfortunately some variation in usage. So you need to check the particular book or notes for the definition being used.
Excerpted from wikipedia:
Two edges of a graph are called adjacent (sometimes coincident) if they share a common vertex.
Similarly, two vertices are called adjacent if they share a common edge.
An edge and a vertex on that edge are called incident.
This terminology seems very sensible to my ear.
An edge "e" in a graph (Undirected or directed ) that is associated with the pair of vertices n and q is said to be incident on n and q, and n and q are said to be incident on e and to be adjacent vertices.
