19. The method of claim 17 wherein the latent semantic space satisfies ∥q k ′−d j ′∥ 2 −∥q k ′−d i ′∥ 2 >0.
17. A method comprising: receiving as a training set, a set of ranked query-document pairs; summarizing global text information from documents in the training set by computing a first matrix; summarizing rank information from the training data by computing a second matrix; applying the first matrix to the second matrix to smooth the second matrix to obtain a third matrix; computing eigenvectors of the third matrix as column vectors of a subspace; and reporting the subspace as a latent semantic space for ranking.