Considering the cost of consistency both the ranking results in initial f 1 and the feedback from f 2 , we define the cost function caused by refining f 1 with f 2 in the (t + 1) th round iteration as where f 1 denotes the initial ranking scores of f 1 .
formally, given a set of candidate templates T S candidate = {T (1) , T (2) , ..., T (n) } ⊂ R m , let f k : T S candidate → R denote the ranking function on the k th feature, where f k ∈ f = {f 1 , f 2 , f 3 }.