2/20 Exponential Moving Average

/*********************************Provided By:      eSignal (Copyright c eSignal), a division of Interactive Data     Corporation. 2008. All rights reserved. This sample eSignal     Formula Script (EFS) is for educational purposes only and may be     modified and saved under a new file name.  eSignal is not responsible    for the functionality once modified.  eSignal reserves the right     to modify and overwrite this EFS file with each new release.Description:            This Indicator plots 2/20 Exponential Moving AverageVersion:            1.0  09/26/2008Notes:    This indicator plots 2/20 exponential moving average. For the Mov     Avg X 2/20 Indicator, the EMA bar will be painted when the Alert criteria is met.Formula Parameters:                     Default:    Moving average source               close    Length                              20 **********************************/var fpArray = new Array();var bInit = false;function preMain() {    setPriceStudy(true);    setStudyTitle("Mov Avg X 2/20");    setCursorLabelName("XAverage");    setColorPriceBars(true);    setDefaultPriceBarColor(Color.black);        askForInput();    var x=0;        fpArray[x] = new FunctionParameter("MASource", FunctionParameter.STRING);	with(fpArray[x++]){        setName("Source of moving average");        addOption("open");         addOption("high");        addOption("low");        addOption("close");        addOption("hl2");        addOption("hlc3");        addOption("ohlc4");         setDefault("close");     }            fpArray[x] = new FunctionParameter("Length", FunctionParameter.NUMBER);	with(fpArray[x++]){        setLowerLimit(1);		        setDefault(20);    }}var xXA = null;function main(MASource, Length) {        var nBarState = getBarState();        if(nBarState == BARSTATE_ALLBARS) {        if (MASource == null) MASource = "close";        if (Length == null) Length = 20;     }          if (bInit == false) {        var xPrice = eval(MASource)();        xXA = ema(Length, xPrice);        bInit = true;    }    if (getCurrentBarCount() < Length) return;        var nHH = Math.max(high(0), high(-1));    var nLL = Math.min(low(0), low(-1));        var nXA = xXA.getValue(0);        if ((nLL > nXA)||(nHH < nXA)) setPriceBarColor(Color.red);        return nXA;}