@emtiyaz 
```
if (V_train.vlen==0 || V_test.vlen==0)
```
means if there's no user records in train or test set, we should not add these the rmse.
For that case, if V_train.vlen==0 but V_test.len!=0 which means cold start user, I ignore these user too.

I add these logical in your matlab code too.