For example, one can train a discriminative classifier to estimate the parameters.
we opted for a simpler approach-we set it equal to the empirical estimate of the expected feature vector x u,v on the training set: 6 where l refers to a document in the training set, t is (as before) a position in the document, h (l,t) and   d (l,t) are the history and the correct DR for this position, respectively.