incidence matrix of a digraph with a self loop When writing the incidence matrix of a digraph, we denote '+1' if the tail of an arc is at the vertex, '-1' if the head is at the vertex. Is it '0' for a self loop at the vertex?

The incidence matrix of a digraph (directed graph) has been defined as follows.

The values for Mij (elements of the incidence matrix)

{ If the arc head is on the vertex => -1 If the arc tail is on the vertex => +1 Otherwise => 0 }

This is how the incidence matrix for a digraph has been defined.

In your question, if it's a self loop, then the value should be 0.