A recommender system tries to predict the potential items that a user might be interested in, based on a history from other users.
So let's consider a so-called item-user or product-customer matrix, as illustrated here:
This is a so-called sparse matrix because only a couple of cells are populated with non-zero values indicating a match between a customer i and a product j. Either by just putting a one in the cell or any other numerical value, for example, indicating the number of products bought or a rating for that particular product j from customer i. Let's call this matrix rui, where u stands for ...
