Why does the function "create_edges_graphs_sparse_relative_distance" create an undirected graph

[xiaohei07]

As the title says, maybe there is a node called A, and its first feature value is 1. Then there is a node called B with 10 first feature value. Now C1-C25 has their first feature values range from 11 to 12. The first feature values of other nodes are greater than 20. (Assuming that the distances between these nodes are all less than diff.)
For node A, through this function, it will build 25 undirected edges for B, C1-C24. For B, it will build 25 undirected edges for C1-C25. And so, the edge will be repeated multiple times
test code as show:

the result is: