string: We build a development data set consisting of 10 randomly selected queries (from TREC 2009, 2010 and 2011 Web tracks) to fine tune parameters, and obtain the following configuration: Œ≤, the trade-off parameter of MMRE defined in Formula 4 is set to 0.5; Œ∑, the parameter that controls the trade-off between Frobenius-norm loss and trace norm loss, is set to 1; the number of dimensions of an expansion term vector (N ) is fixed to 30; K, the number of expansion term candidates, is set to 100; the parameter that controls the trade-off between relevance and nonredundancy in MMREQ (Bouchoucha, Liu, and Nie 2014) is set to 0.6.