Possible bug: edge properties not correctly propagated with global attachment

[meiertgrootes]

The globala attachement method uses dgl.to_simple to remove potential duplicate edges. To this end, it reasssigns the result to agent_graph. Default behaviour of .to_simple(), however, is to NOT copy edge properties. This imolies that all graph edge properties are being wiped on use of global_attachment().

TO DO:

• [ ]: check dgl.to_simple behaviour
• [ ]: verify that this leads to unintended ressults in dgl_ptm

possible fix:

• [ ]: own, adjacency matrix based global attachment implementation

[SarahAlidoost]

@meiertgrootes according to dgl.to_simple doc, copy_ndata is True by default whereas copy_edata is False! I added a test to check this and fixed it by adding copy_edata=True to to_simple() function in global_attachment, see here.