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Because the ALS algorithm generates a full matrix, it is always able to make recommendations.
There are two k dimensional vectors which are referred to as ¡°factor¡±.
𝑥_𝑢 is k dimensional vectors summarizing¡¯s every user u.
𝑦_𝑖 is k dimensional vectors summarizing¡¯s every item i.
Use stochastic gradient descent to minimize the squared error between the predicted rating the actual rating,
Here, 𝜆 is the regularization factor, which is used to address the over fitting issue, is referred as weighted- 𝜆-regularization. The default value of 𝜆 is 1.
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