How to indicate loops in the incidence matrix?

Question

Mathematics

I froze when I asked myself this question. I got on Wikipedia and met mutually exclusive paragraphs there. (I'm talking about the Russian wiki). It states that the incidence matrix can be applied to any graph, even if they have loops. But it says that each column must have either two 1s, or 1 and -1. That eliminates the presence of loops.

Answer 1

General rule for loops: count twice.
Specifically on this issue: analysis with an example .