This projection can be thought of as a multivariate linear regression problem with weight matrix G, one weight vector per dimension of u i .
a related line of research looked into predicting helpfulness of reviews in the hope of promoting those with better quality, where helpfulness is usually defined as some function over the percentage of users who found the review to be helpful (Kim et al., 2006;Liu et al., 2007;Danescu-Niculescu-Mizil et al., 2009).