Recommending items that have rarely/never been viewed by users is a bottleneck for collaborative filtering (CF) based recommendation algorithms. Previously, item content representation (mostly in textual form) has been used as auxiliary information for learning latent factor representations. Embodiments learn latent factor representation for content items based on modelling an emotional connection between user and content item and based on implicit user feedback regarding the content item.
Please help me write a proper abstract based on the patent claims. CLAIM: 1. A computer-implemented method for ranking items, comprising: receiving an M by N matrix, wherein each of the M rows represents a user and each of the N columns represents an item, wherein each entry in the matrix represents implicit feedback given by one of the M users with regard to one of the N items, and wherein at least one entry in the matrix is undefined; receiving an N dimensional vector, wherein each entry represents a content-based estimation of an emotional response that one of the N items evokes; generating, based on the N dimensional vector of estimated emotional responses and the received M by N matrix of implicit feedback, an M by K user matrix and a K by N item matrix that, when multiplied together, produces an M by N matrix of relevance scores, wherein each relevance score defines a relevance of one of the N items to one of the M users; and determining, for one of the M users, a ranked-list of item recommendations based on the generated M by K user matrix and the generated K by N item matrix. 2. The computer-implemented method of claim 1, wherein generating the K by N item matrix includes generating an N by N transformation matrix that when multiplied by the N dimensional vector of estimated emotional responses generates the K by N item matrix. 3. The computer-implemented method of claim 2, wherein generating the M by K user matrix and N by N transformation matrix includes: randomly seeding values of the M by K user matrix and the N by N transformation matrix; and iteratively updating the M by K user matrix and the N by N transformation matrix based on minimizing an objective function, wherein the objective function is based on the N dimensional vector of estimated emotional responses and the received M by N matrix of implicit feedback. 4. The computer-implemented method of claim 3, wherein the objective function is defined in terms of the M by K user matrix and the N by N transformation matrix, and wherein iteratively updating the M by K user matrix and the N by N transformation matrix includes: repeating, until a number of iterations has been reached or a convergence has been detected: for each of the M users: set the M by K user matrix to a sum of the M by K user matrix and a partial derivative of the objective function taken with respect to the M by K user matrix, and, for each of the N items, set the N by N transformation matrix to the sum of the N by N transformation matrix and a partial derivative of the objective function taken with respect to the N by N transformation matrix. 5. The computer-implemented method of claim 3, wherein the objective function is based on maximizing a mean reciprocal rank function, wherein the mean reciprocal rank function orders items based on relevance to the user. 6. The computer-implemented method of claim 1, wherein the implicit feedback given by the one of the M users with regard to the one of the N items comprises a unary implicit feedback. 7. The computer-implemented method of claim 6, wherein the unary implicit feedback includes an indication that the item was liked, an indication that the item was experienced, an indication that the item was experienced for a defined amount of time, or an indication that the item was experienced for a defined percentage of time. 8. The computer-implemented method of claim 1, wherein the item is a video, photo, audio, or text. 9. The computer-implemented method of claim 1, wherein all items of at least one column of the received M by N matrix are undefined. 10. The computer-implemented method of claim 1, wherein each entry of the N-dimensional vector of estimated emotional responses comprises a real number value. 11. The computer-implemented method of claim 10, wherein each of the real number values is derived from a syntactic structure of the corresponding item. 12. The computer-implemented method of claim 11, wherein for an image or video item, the syntactic structure comprises pixels, wherein for a text item the syntactic structure comprises characters or words, and wherein for an audio item the syntactic structure comprises an audio waveform. 13. The computer-implemented method of claim 1, wherein the ranked-list of item recommendations is further based on implicit feedback of other M users. 14. A computing apparatus for ranking items, the computing apparatus comprising: a processor; and a memory storing instructions that, when executed by the processor, configures the apparatus to: receive an M by N matrix, wherein each of the M rows represents a user and each of the N columns represents an item, wherein each entry in the matrix represents implicit feedback given by one of the M users with regard to one of the N items, and wherein at least one entry in the matrix is undefined, receive an N dimensional vector, wherein each entry represents a content-based estimation of an emotional response that one of the N items evokes, generate, based on the N dimensional vector of estimated emotional responses and the received M by N matrix of implicit feedback, an M by K user matrix and a K by N item matrix that, when multiplied together, produces an M by N matrix of relevance scores, wherein each relevance score defines a relevance of one of the N items to one of the M users, and determine, for one of the M users, a ranked-list of item recommendations based on the generated M by K user matrix and the generated K by N item matrix. 15. The computer-implemented method of claim 14, wherein generating the K by N item matrix includes generating an N by N transformation matrix that when multiplied by the N dimensional vector of estimated emotional responses generates the K by N item matrix. 16. The computer-implemented method of claim 15, wherein generating the M by K user matrix and N by N transformation matrix includes: randomly seeding values of the M by K user matrix and the N by N transformation matrix; and iteratively updating the M by K user matrix and the N by N transformation matrix based on minimizing an objective function, wherein the objective function is based on the N dimensional vector of estimated emotional responses and the received M by N matrix of implicit feedback. 17. The computer-implemented method of claim 16, wherein the objective function is defined in terms of the M by K user matrix and the N by N transformation matrix, and wherein iteratively updating the M by K user matrix and the N by N transformation matrix includes: repeating, until a number of iterations has been reached or a convergence has been detected: for each of the M users: set the M by K user matrix to a sum of the M by K user matrix and a partial derivative of the objective function taken with respect to the M by K user matrix, and, for each of the N items, set the N by N transformation matrix to the sum of the N by N transformation matrix and a partial derivative of the objective function taken with respect to the N by N transformation matrix. 18. The computer-implemented method of claim 17, wherein the M by K user matrix and the K by N item matrix comprise latent factor representations of an M by N user-item relevance matrix. 19. The computer-implemented method of claim 18, wherein the ranked-list of item recommendations for the user is determined based on sorting, in descending order, for each row of the K by N item matrix, a dot product of a column of the M by K user matrix that corresponds to the user with the row of the K by N item matrix. 20. A non-transitory computer-readable storage medium for ranking items, the computer-readable storage medium including instructions that when executed by a computer, cause the computer to: receive an M by N matrix, wherein each of the M rows represents a user and each of the N columns represents an item, wherein each entry in the matrix represents implicit feedback given by one of the M users with regard to one of the N items, and wherein at least one entry in the matrix is undefined; receive an N dimensional vector, wherein each entry represents a content-based estimation of an emotional response that one of the N items evokes; generate, based on the N dimensional vector of estimated emotional responses and the received M by N matrix of implicit feedback, an M by K user matrix and a K by N item matrix that, when multiplied together, produces an M by N matrix of relevance scores, wherein each relevance score defines a relevance of one of the N items to one of the M users; and determine, for one of the M users, a ranked-list of item recommendations based on the generated M by K user matrix and the generated K by N item matrix.