A Question on link splitting

[Razavi1999]

I was wondering why you are returning upper triangular portion of the edges in at this link.
If you could tell me the theory of why this is happening in here, I would really appreciate that.

[rusty1s]

train_test_split_edges assumes undirected graphs, and so we solely split on the upper triangular portion of the graph so that reverse edges do not land in different splits.