This is done when the RNN component is sequentially fed by the embedding vectors {v t }, and iteratively compute a hidden state vector {h t } based on the previous hidden state and the current input embedding vector, using some function f .
moreover, the output of this unit {o t } in each timestamp t, is computed based on the current hidden state using a function g. we use a GRU unit as a RNN as presented by Cho et al.