$$ \sqrt{\frac{\sum_{i=1}^{n}\left(\hat{r}_{ui}-r_{ui}\right)^2}{n}} $$
$\hat{r}$
pc@user$ pandoc --versionpandoc 1.19.2.1Compiled with pandoc-types 1.17.0.4, texmath 0.9, skylighting 0.1.1.4Default user data directory: /home/user/.pandocCopyright (C) 2006-2016 John MacFarlaneWeb: http://pandoc.orgThis is free software; see the source for copying conditions.There is no warranty, not even for merchantability or fitnessfor a particular purpose.