If the question state:
A connected and undirected graph, then does this graph allow loop or multiple edges?
I searched over the internet, but some allow, some don't. It's so confusing. Any idea? Thank you.
If the question state:
A connected and undirected graph, then does this graph allow loop or multiple edges?
I searched over the internet, but some allow, some don't. It's so confusing. Any idea? Thank you.
Most of the results that are covered in a graph theory course concern "simple" graphs, that in general do not permit self-loof or multiple edges. Graphs that allow multiple edges between two vertices are known as multi-graphs. Graphs that permit self-loops are sometimes called pseudo-graphs.
The restriction on multiple edges between two vertices is sometimes weakened for directed graphs so that both $(a,b)$ and $(b,a)$ can be included in the edge set of the directed graph.