Node representation update in a Message Passing Neural Network (MPNN) layer. Node x 0 {\displaystyle \mathbf {x} _{0}} receives messages sent by all of his immediate neighbours x 1 {\displaystyle \mathbf {x} _{1}} to x 4 {\displaystyle \mathbf {x} _{4}} . Messages are computing via the message function ϕ {\displaystyle \phi } , which accounts for the features of both senders and receiver.