where ‖ {\displaystyle \Vert } denotes vector concatenation, 0 {\displaystyle \mathbf {0} } is a vector of zeros, Θ {\displaystyle \mathbf {\Theta } } is a matrix of learnable parameters, GRU {\displaystyle {\text{GRU}}} is a GRU cell, and l {\displaystyle l} denotes the sequence index.