Illustration of an LSTM. The input x_k is used in combinations with the output h_k−1 and the cell state c_k−1 from the previous time step k − 1 to produce the output h_k for the k-th time step. The cell state c_k acts as memory and transports information through the cell, where the forget gate f_k , input gate i_k , and gate g_k update information in the cell state. The output gate, based on the previous output h_k−1 and input x_k in combination with information from the cell state provides the new output h_k. For more information, see Eqs. (11)–(16).