Therefore, by incorporating PRO loss (Xu et al., 2013), the loss function for the instance x i is defined as follows: (1) where e t refers to the emotion belonging to relevant emotion set R i or the threshold Θ of instance x i while e s refers to the emotion which is less relevant than e t denoted as ≺.
(e t , e s ) represents four types of emotion pairs: i.e., (relevant, relevant), (relevant, irrelevant), (relevant, threshold), and (threshold, irrelevant).