See also the following links:

▎ENGLISH

Matrix Factorization (Recommender Systems) - Wikipedia
▸ https://en.wikipedia.org/wiki/Matrix_factorization_(recommender_systems)

Recommendation Systems: Collaborative Filtering using Matrix Factorization — Simplified
▸ https://medium.com/sfu-cspmp/recommendation-systems-collaborative-filtering-using-matrix-factorization-simplified-2118f4ef2cd3

Introduction to Matrix Factorization for Recommender Systems
▸ https://osf.io/pnd5w/download

▎日 本 語

推薦システム初心者におすすめの手法「行列分解」とは？
▸ https://codezine.jp/article/detail/14280

Matrix Factorizationとレコメンドと私
▸ https://qiita.com/michi_wkwk/items/52660778ad6a900965ee

推薦システムのアルゴリズム （p. 64)
▸ https://kamishima.net/archive/recsysdoc.pdf