A growing number of retailers offer products/services via the Internet as well as at brickandmortar stores. These multiple marketing channels increase the opportunity for customers to buy. In addition, retailers can analyze detailed customer information gained from multichannel shopping in order to improve their service quality. In view of these facts, we develop a specialized recommender method based on the weighted nonnegative matrix factorization to expand the number of customers that make

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... e of multiple marketing channels. Our method effectively uses the similarities of customers and products to promote customers' multichannel shopping. Computational results demonstrate that our method delivers better recommendation performance than the existing recommender methods.