Keltner band (channel) top
len - lookback period
atrs - number of ATRs
It's not clear that there's a "standard" way to implement Keltner channels. The center line could be either a simple or an exponential average. The ATR might use a simple average, EMA, or Wilder's smoothing. This function is a shortcut for EMA(C, len) + atrs * EMA(TR, len).
This indicator supports ultra-fast one-pass calculation when used in the Data Section with a non-variable length.