How is edge_update in GatConv being called?

[colintle]

Hi I am looking to understand the math behind GatConv. After looking at the source code, I see a function called edge_update with alpha_j and alpha_i as parameters. In the forward method of GatConv, we call edge_updater with alpha passed in as parameter. I know there is some jinja template that gets rendered to that references to the edge_updater in GatConv, but I don't understand how alpha_j and alpha_i are being initialized?