with xi ∈ X is the feature of node i, ei,j ∈ E is the edge feature between nodes i and j, γ and ϕ are differentiable functions such as MLP (neural networks), is a permutation invariant function (most common is ) and t is the t th layer in the GNN. Informally, the message passing operation exchanges information between nodes j and the node i within the neighbourhood of i given through j ∈ N (i). Information on a node's neighbourhood is contained within adjacency matrix A. During each layer t of the GNN, node embeddings are updated from x (t-1) i to x (t) i .