In the simplest case, children nodes are combined into their parent node using a weight matrix W which is shared across the whole network, followed by a non-linear function g(•).
given the left child node vector h L ∈ R d and right child node vector h R ∈ R d , their parent node vector h P ∈ R d will be formalized as: where W ∈ R d×2d and g is a non-linear function as mentioned above.