{_xAverage - Exponential Moving Average that allows for
 variable lookback.
 by Alex Matulich, Unicorn Research Corporation}

Inputs: Price(NumericSeries), Length(NumericSimple);

Variables:  w(0), xlen(0), pv(0);

if CurrentBar <= 1 then pv = Price else pv = _xAverage[1];
if xlen <> Length or CurrentBar <= 1 then begin
    w = 2 / (Length + 1);
    xlen = Length;
end;
_xAverage = w * Price + (1 - w) * pv;