Let Γ be a general graph (which may be the underlying graph of a quiver).
Given two vertices 𝑣,𝑤∈V(Γ), the adjacency number|Γ(𝑣,𝑤)| is the number of arcs 𝑣→𝑤.1
If the vertices are enumerated 𝑣1,…,𝑣𝑟, then these may be collected in an adjacency matrix𝐴Γ=(𝑎𝑖𝑗) where graph
Thinking of A(Γ) as a multiset with characteristic function 𝜒A(Γ), this is just 𝜒A(Γ)(𝑣,𝑤). The notation is preferred since it gives a uniform treatment to quivers and their underlying graphs. ↩