We use • for function composition, and ∆ p for the set of one hot vectors in dimension p. Given a training set S = {(X n , y n )} N n=1 of pair-wise data, where X ∈ X is the text sequence, and y ∈ Y is its corresponding label.
y is a one hot vector in single-label problem and a binary vector in multi-label problem, as defined later in Section 4.1.