The transition equations of node j in the bottom-up model are formulated as follows: where x j is the original input vector of node j, E denotes the parameter matrix for transforming this input post,x j is the transformed representation of j, [W * , U * ] are the weight connections inside GRU, and h j and h s refer to the hidden state of j and its s-th child.
h S denotes the sum of the hidden state of all the children of j assuming that all children are equally important to j.