Exercise

# RMSE as ALS alternates

As you know, ALS will alternate between the two factor matrices, adjusting their values each time to iteratively come closer and closer to approximating the original ratings matrix. This exercise is intended to illustrate this to you.

Matrix `T`

is a ratings matrix, and matrices `F1`

, `F2`

, `F3`

, `F4`

, `F5`

, and `F6`

are the respective products of ALS after iterating 2, 3, 4, 5, and 6 times respectively. Follow the instructions below to see how the RMSE changes as ALS iterates.

Instructions

**100 XP**

- Use
`getRMSE(pred_matrix, actual_matrix)`

to calculate the RMSE of`F1`

. - Put
`F2`

,`F3`

,`F4`

,`F5`

, and`F6`

into one list called`Fs`

. - Complete the
`getRMSEs(listOfPredMatrices, actualValues)`

function to calculate the RMSE of each matrix in the`Fs`

list.