Typically this gold function is BLEU (Papineni et al., 2002), though there are several common alternatives (Lavie and Denkowski, 2009;Melamed et al., 2003;Snover et al., 2006;Chiang et al., 2008a).
we want to find a weight vector w such that H w behaves "similarly" to G on a candidate space s. we assume a loss function l s (H w , G) which returns the real-valued loss of using scoring function H w when the gold scoring function is G and the candidate space is s. we may say the goal of tuning is to find the weight vector w that minimizes loss.