I am trying to calculate coverage metrics for a recommender system that I have designed. This blog post talks about how to do it. I had some difficulties in understanding the same. It says that These metrics will be for user u of U users over n items out of N potential items in a recommendation list L. Each item has a content vector C of length c ... My difficulty arises in understanding N and U. Is U the total number of users? Secondly, what does N potential items mean? Is it the list of all items that are present or is it a subset of all the items present?
I am using the Python LightFM package to generate the recommendations