I want to compute adjusted cosine similarity value in an item-based collaborative filtering system for two items represented by a and b respectively. these items are represented by two vectors a={2,3,1,0} and b={1,0,4,2}. I know how cosine similarity works but i am stuck with adjusted cosine similarity approach. we are working on a collaborative filtering recommender system where we need to find similar items using adjusted cosine similarity. Those who are working in CF recommender systems please guide me.