Trend Analysis Index (TAI)

/*********************************Provided By:      eSignal (Copyright c eSignal), a division of Interactive Data     Corporation. 2009. 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:            Trend Analysis Index    Version:            1.0  05/20/2009     Formula Parameters:                     Default:    AvgLen                              28    TAILen                              5    Source of TAI                       Close    Notes:    In essence, it is simply the standard deviation of the last x bars of a     y-bar moving average. Thus, the TAI is a simple trend indicator when prices     trend with authority, the slope of the moving average increases, and when     prices meander in a trendless range, the slope of the moving average decreases.**********************************/var fpArray = new Array();var bInit = false;function preMain() {    setPriceStudy(false);    setStudyTitle("Trend Analysis Index");    setCursorLabelName("TAI");    var x = 0;    fpArray[x] = new FunctionParameter("AvgLen", FunctionParameter.NUMBER);    with(fpArray[x++]) {        setLowerLimit(1);        setDefault(28);    }        fpArray[x] = new FunctionParameter("TAILen", FunctionParameter.NUMBER);    with(fpArray[x++]) {        setLowerLimit(1);        setDefault(5);    }        fpArray[x] = new FunctionParameter("sPrice", FunctionParameter.STRING);	with(fpArray[x++]){        setName("Source of TAI");        addOption("open");         addOption("high");        addOption("low");        addOption("close");        addOption("hl2");        addOption("hlc3");        addOption("ohlc4");         setDefault("close");     }    }var xTAI = null;function main(sPrice, AvgLen, TAILen) {var nBarState = getBarState();var nTAI = 0;    if (nBarState == BARSTATE_ALLBARS) {        if (sPrice == null) sPrice = "close";        if (AvgLen == null) AvgLen = 28;        if (TAILen == null) TAILen = 5;    }    if (bInit == false) {        xTAI = efsInternal("Calc_TAI", sPrice, AvgLen, TAILen);        bInit = true;    }    nTAI = xTAI.getValue(0);    if (nTAI == null) return;    return nTAI;}var bSecondInit = false;var xSMA = null;var xHH = null;var xLL = null;var xPrice = null;function Calc_TAI(sPrice, AvgLen, TAILen) {var nRes = 0;    if (bSecondInit == false) {        xPrice = eval(sPrice)();        xSMA = sma(AvgLen, xPrice);        xHH = upperDonchian(TAILen, xSMA);        xLL = lowerDonchian(TAILen, xSMA);        bSecondInit = true;    }    if (xHH.getValue(0) == null) return;    nRes = (xHH.getValue(0) - xLL.getValue(0)) * 100 / xPrice.getValue(0);    return nRes;}