This message aims at showing an example of computing and plotting custom indicator with R.
The chosen indicator is RSI.
I hope that the code is self-explanatory.
It plots below the chart:
1) quantmod (TTR)'s built-in RSI
2) with addTA(): custom RSI built as a xts object
3) with newTA(): custom RSI built as a function.
If you know better ways to do it, do not hesitate to comment.