Bollinger Bands® (John Bollinger) — a period-bar simple moving average
(the middle band) with an upper/lower band at ±stdDev population standard
deviations. Appends three columns (${prefix}Middle / ${prefix}Upper /
${prefix}Lower); the warm-up rows and any flat window (σ = 0) emit
undefined bands. One rolling pass (avg + stdev) over a bar-count window.
Bollinger Bands® (John Bollinger) — a
period-bar simple moving average (the middle band) with an upper/lower band at ±stdDevpopulation standard deviations. Appends three columns (${prefix}Middle/${prefix}Upper/${prefix}Lower); the warm-up rows and any flat window (σ = 0) emitundefinedbands. One rolling pass (avg + stdev) over a bar-count window.