An improved item-based KNN predictor

Today, I revise the item-based KNN predictor and get RMSE = 0.8730 in quiz with other 39 predictors.

The classical item-based kNN will firstly calculate similarity between item i and j by：



The, the rating r(u,i) will be predicted by:



However, I revise this predictor by:



This predictor can produce more accurate prediction by choosing adequate alpha