How to convert N node indices in edge_index to 2 x (N*N) edge_index

[Nokimann]

Let edge_index be [[1, 3, 5, 5], [5, 3, 1, 3]]

There are 1, 3, and 5 node indices.

I need to convert from the above edge_index to [[1, 3, 5, 1, 3, 5, 1, 3, 5], [1, 3, 5, 3, 5, 1, 5, 1, 3]] without for loop,
which is the partially-connected node indices are then all linked, including themselves.

[Nokimann]

I found the answer from here

a = torch.tensor([1, 3, 5, 5])
a = torch.unique(a)
torch.cartesian_prod(a, a)