Stock Constrained Recommendation in Tmall

A large number of recommender systems have been developed to serve users with interesting news, ads, products or other contents. One main limitation with the existing work is that they do not take into account the inventory size of of items to be recommended. As a result, popular items are likely to be out of stock soon as they have been recommended and sold to many users, significantly affecting the impact of recommendation and user experience. This observation motivates us to develop a novel aware recommender system. It jointly optimizes the recommended items for all users based on both user preference and inventory sizes of different items. It requires solving a non-smooth optimization involved estimating a matrix of nxn, where n is the number of items. With the proliferation of items, this approach can quickly become computationally infeasible. We address this challenge by developing a dual method that reduces the number of variables from n^2 to n, significantly improving the computational efficiency. We also extend this approach to the online setting, which is particularly important for big promotion events. Our empirical studies based on a real benchmark data with 100 millions of user visits from Tmall verify the effectiveness of the proposed approach.