Builtin functions

DGL builtin functors

Message functions

copy_src(src, out)	Builtin message function that computes message using source node feature.
copy_edge(edge, out)	Builtin message function that computes message using edge feature.
src_mul_edge(src, edge, out)	Builtin message function that computes message by multiplying source node features with edge features.

Reduce functions

sum(msg, out)	Builtin reduce function that aggregates messages by sum.
max(msg, out)	Builtin reduce function that aggregates messages by max.