In this blog, I will follow Recommendations in TensorFlow: Create the Model and study basic yet powerful recommendation algorithm, collaborative filtering using tensorflow version 1.

**What you learn**

- collaborative filtering
- Weighted alternating least squares (WALS) method
- tensorflow (v1.15.0)

In particular, this blog will show that the WALS method is pretty sensitive to the choice of weights (linear weights v.s. log weights vs uniform weights). I will use `movieLens 100k`