1 requires that a non-pivot w that co-occurs with a pivot c in the document d is assigned a higher ranking score as measured by the inner-product between c S and w S than a nonpivot w * that does not occur in d. We randomly sample k non-pivots from the set of all source do-main non-pivots that do not occur in d as w * .
we use the marginal distribution of non-pivots p(w), estimated from the corpus counts, as the sampling distribution.